I don't refer to her as my oldest friend. There comes a point in a girl's life (some time after she has reluctantly accepted that she's not a girl any longer) when such descriptions are less than kind. She is instead my friend of longest standing.

We met on our second day at senior school when we literally bumped into each other in the dinner queue. The reason we bumped into each other was that we both had our noses in a book instead of looking where we were going. In the moment of discovery that we were both reading a Captain W E Johns' Biggles Book, was our friendship formed; a friendship still strong after – well, perhaps I had better not say after how many years.

She was the first person to know I was bi-polar. I only wish she'd thought to tell me at the time.

It was only when we watched the Stephen Fry documentary together more than thirty years later that she realised that I still didn't know.

Of course, it wasn't called bi-polar back when we were at school.

"I knew you were a manic depressive when you were thirteen." She said (shockingly). My mouth open, I just stared at her. "Yes" she said, "I read Spike Milligan's autobiography and thought "Ah, now that explains Mary.""

So my best friend has always known, has always accepted it and has just given me all the space I needed to be both the life and soul of the party and to withdraw totally for weeks or months at a time. It has never affected our friendship in the smallest degree.

Now that we both know a lot more about the condition, she's also invaluable for telling me when I'm going down and need to make an appointment to see the doctor. Because I don't always know.

It's not just my lovely friend (of longest standing) who assists me in managing things. I have a couple of book club friends who keep an eye on me, my husband always knows better than I do what's happening and gradually a few of my business networking friends are becoming close enough to know.

No – I have no idea how they know. They just say they can see it in my face.

These days, Moodscope is invaluable. I look at the pattern over the last three months, with all the yellow dots for the comments and can see the point at which I said "Oops – better start the fluoxetine again". I can fool myself into thinking I'm better, but then I play those cards and know better. Still down: still need to take it easy. Grrr.

So when we say of someone "They know me better than I know myself" – yes, we're probably right. It's not just mother knows best; it's our friends and family probably know best. But we do need to trust them. They're right. We know they're right. Blast it!

Mary

A Moodscope member.