Covid restrictions also make it substantially scarier, with no audience to counterbalance the effect of that one stark piece of furniture, bathed in a bright white spotlight.

I had expected to have a bit of a chit chat with host Clive Myrie before embarking on my best Judith Keppel impersonation, but that bit comes after you’ve done your specialist subject round.

So you basically go straight onto the cold, hard leather with no preamble whatsoever. It is genuinely terrifying.

The feeling in the pit of my stomach was on a par with how I felt on the morning of my GCSE maths exam – and I am less than functionally innumerate.

And no, we aren’t told what we are going to be asked beforehand just because it’s the celebrity version. If bloody only!

I think I had it worse than all the others because I was last alphabetically, which meant I had to sit and watch everyone else being tortured before meeting the executioner myself.

Obviously I can’t give away any spoilers, but I soon realised that the specialist subject round was going to be the least of my worries. At least you can revise for that.

It’s the general knowledge that’s the killer.

I mean, I’m OK at Trivial Pursuit – but this is nothing like that. You don’t get to mull over the question at your leisure or subtly ask Siri when everyone else is still squabbling over whether it was Heracles or Hercules.

You’re completely on your tod up there. Exposed. It’s like being on Everest in your bra and knickers.

And there are no prompts. No Chase-like a, b or c to choose from or the Millionairesque chance to go 50:50.

You either know the answer or you don’t. And that’s if you’ve managed to concentrate hard enough to actually take the question in. Some of them are so wordy they make University Challenge look like a game of KerPlunk.

But this is the real rub: Because of the chair’s occultish habit of making you forget your own mother’s name, you soon find out – to your abject horror – that you don’t know the answers even when you do!

It must be the time pressure. Just look at some of the ridiculous answers given on Family Fortunes over the years. (A friend once went on and was asked to name a fruit with a stone in it. She replied: “scone”.)

Similarly, at one point during the two minutes of hell, which felt like a fortnight, Clive asked me: “How many legs does an insect have?” For reasons I will never be able to fully explain, I replied: “four”.

It’s the chair, I tell you! It literally halves your wits. You become a halfwit as soon as you sit in it. So you basically need a brain double the size of everyone else’s if you are to stand any hope in hell of getting over 20. Get over 30 and you are basically the lovechild of Albert Einstein and Carol Vorderman.

I can honestly say that I genuinely knew the correct answers to all the questions I got wrong, bar one – I just couldn’t summon them because of the sheer horror of the occasion.

As I had decided that I wouldn’t pass on anything (if it’s a draw, your number of passes counts against you), I came out with some absolute howlers. I can’t tell you how happy I was to be on the plane home – even though I didn’t embarrass myself too badly in the end.

Of course, I spent several days afterwards wishing I could go back to the beginning and do it all over again, knowing then what I know now.

Trouble is, unlike Marty and Doc – I don’t have a time machine.

Celebrity Mastermind is on BBC One at 6.35pm tonight