I sometimes wonder about my parallel life: the one in which I attended drama school, became a respected actor, travelled the world and ended up marrying Louis Theroux after meeting him at an awards ceremony. The life in which I didn’t develop anxiety and agoraphobia.

In 1995, aged 23, after years of auditions, my application had been accepted for the Royal Welsh College of Music & Drama. My desire to act since the age of eight was firmly cemented and my dreams were coming to fruition. I was living in London so I’d arranged some viewings of potential digs. My boyfriend and I decided to make a trip of it and planned an extended scenic route – a concept now incomprehensible. But by the time we left, I was getting nervous.

Anxiety and I were no strangers. At 20, my life became one long panic attack. Ironically, I was more likely to experience claustrophobia at this point and I’d frequently head to London’s West End for relief from my anxiety. But by the time I was off to drama school, I was feeling better, thanks to some CBT and beta-blockers. I was confident it was all behind me and excited about what lay ahead. The nerves I experienced that day, as everyone assured me, were normal.

We headed down the motorway – music loud, chatting; me eating the cheese and piccalilli sandwiches we’d packed for the journey. But I’d barely finished the last one when I had the mother of all panic attacks and they made a reappearance over my boyfriend’s van.

That was the moment my world shrunk smaller than the set of The Truman Show. The moment I became agoraphobic. And 25 years later – I still am.

It’s a misconception that agoraphobia is a fear of open spaces. Though the word originates from the Greek for “fear of the market square”, according to the NHS website it is “a fear of being in situations where escape might be difficult or that help wouldn’t be available if things go wrong”. Although true, that is a simplistic description of a complex beast whose manifestation is particular to each person. It can morph and shapeshift. Worlds can shrink and enlarge like pufferfish. But generally (though not always) it’s an unfortunate upgrade from the already debilitating panic disorder. It’s the promotion no one wants. At its core, it’s a phobia of having panic attacks (a very real, terrifying physical reaction) in triggering situations, leading to avoidance. It is, ultimately, a fear of fear.

When not in the throes of a deadly pandemic, I do go out. Agoraphobics are not all housebound – that’s another fallacy. I love going out and about. But I’ve also developed an irrational system of imagined borders that depict where I can and cannot go.

Please don’t expect it to make sense. That’s the whole point. It doesn’t. On one hand, I’m a rational person who friends come to for solid advice; someone who’s been a director of a company for 20 years and who has written a novel. On the other, I think I may die because I’ve passed through the traffic lights on Liverpool Road, crossing the line of my invisible boundary.

The reasoning behind choosing the “safe” areas is also illogical. Some nearer destinations are out of bounds or a scarier prospect than somewhere further yet familiar. But to clarify, none are far from my house. I’m trapped within the constraints of my hometown – the only occasion where the term “Madchester” would be acceptable. My restrictions aren’t limited to the where but also the when. The only thing worse than a journey is a journey with bad traffic. The vision of red brake lights ahead is a certain trigger. Overheating, nausea, dizziness, palpitations and derealisation are all exacerbated by the fact I can’t escape.

Of course, this isn’t a continual state. If you met me, you probably wouldn’t suspect any of this. Most of the time I even forget I’m like this myself. Until I receive an invitation to something I’d like to attend. If it’s outside where I feel comfortable, I contemplate if it’s manageable. I investigate, gather further information, such as parking and other events happening that would increase traffic. Whereas the average person may think, “Oh yes, I’m meeting such-and-such in half an hour,” I would have to practise beforehand, attempt missions to the destination; some successful, some failed.

Hopefully, the invite would be a casual one with no pressure. But if someone is relying on me or travelling a distance, my worries intensify, forcing me to add multiple disclaimers and caveats. I am certain I’m considered flaky or selfish, but the reality is the opposite. I don’t want to let people down. So, more often than not I reject the offer despite my desperation to go and the reality being that most likely I’d have been fine.

Imagine what it’s like dating. I’ve had relationships. I’ve been in love. But I also appreciate it’s difficult for the other person. When talking to potentials online, I dread making the announcement. But then that can create a horrifying lead-up where I declare that there is something so awful about me I need to tell them, that when I do, they’re usually just relieved I’m not a convicted killer. The catch-22 is that being with someone helps. I feel safer with a person I trust and love; someone who would be there for me if I collapsed in M&S, which in turn would reassure me that I wouldn’t collapse in M&S.

My mum was my safety person. I could even travel from London to Manchester with her and go to the seaside. When she died five years ago, followed by my dad a few months later, it wasn’t just agonising grief I was dealing with, but my capacity to negotiate the world had gone, too. The pufferfish deflated to the size of an anchovy. I was metaphorically cast adrift, with the additional misfortune of potentially never being able to see the sea again.

What about now? At the beginning of March, I started self-lockdown before the lockdown was a thing. Panic disorder, agoraphobia and Covid-19 is quite the cocktail that on a menu would be called “The Life Ruiner”. Going outside was no longer an option. For the first few weeks, my anxiety rocketed, culminating in continual panic attacks and more hand washing than Lady Macbeth. Irrational fears I’ve carried for 25 years became a reality. Going out had a tangible threat. A friend rang me when lockdown came into force and said, “You’ve been waiting for this moment your whole life.”

But the fact is, the majority are worried about the virus. I see tweets from people experiencing anxiety for the first time, and even agoraphobia. A friend recently had his first panic attack. It’s strange being more on a level with the norm. If you’re suffering, I can assure you, it is transient. No state of panic or anxiety is sustainable. Yes, my overall disorder has lasted, but it’s not consistent, otherwise I’d now be living at Warwick Service Station after once having an episode there, convinced I could neither continue the journey, nor go back home.

The pandemic has forced us to reassess our lives. I wonder if this will be the turning point for me: an extreme-exposure therapy session. I long for the weight to be lifted. When I imagine it is all over, going places doesn’t seem a scary prospect any more. The simple fact of not potentially contracting a deadly virus would make a jaunt to Manchester city centre a total breeze. For the first time in a long while I am optimistic.

Yes, life with anxiety and agoraphobia is excruciating at times. It’s often saddening and exhausting and frustrating. But I don’t look back and wish it had all been different because, well, what’s the point in that? Contrary to what some believe, it’s not a choice. I’d rather laugh at its absurdity and remain hopeful it will change for the better while making peace with the fact it may not.

Going back to that day in 1995 – if I’d made the journey and attended drama school, the highlights of my career could have been a bit part on Casualty followed by a panto run in Blackpool. I wouldn’t have made the friends I have or experienced the same relationships. If I hadn’t had endless therapy, I wouldn’t understand the complexities of humans to the extent I do, enabling me to write my book. And as for Louis Theroux – well, we’re all allowed one regret.

If I Can’t Have You by Charlotte Levin is published on 9 July (£14.99, Mantle). Buy it for £13.04 at guardianbookshop.com