There was a really, really good documentary on OCD on Channel 4 a couple of weeks ago. I think the presenter was Jon Richardson but I am not certain. I was completely startled by how people with extreme OCD can end up. They get to the point where the condition completely overtakes their cognition. They can't leave the house, they can't do anything. Some of them end up incontinent because they can't bring themselves to go into the bathroom.
There was a lady in it talking about her son. OCD runs in her family. She herself, when she comes into her house after a shopping trip, has to completely change all her clothes in the entrance hallway of her home so she is not contaminating the main part of her home. Then when she puts the shopping away, she has to wipe down all the food packaging before it can go in the fridge.
Anyway she was leafing through this dossier about her son. He went to Oxford and got a double first class degree (which is very rare, it's essentially doing two degrees at once and achieving first class honours in both subjects), and went on to study towards a PhD - it ws in one of the chemical sciences. It was at this point that his OCD kicked in. He got to the point where he couldn't sit or sleep and used to spend all his time pacing around.
She then showed his suicide note. What he did was to go out and buy a liquifier and get a load of yew tree branches (which are highly poisonous) and liquify them and drink them. His suicide note gave a brief apology and said that his close friends and family would understand why, and it finished with a detailed list of who the person who found his body needed to contact, including phone numbers and so on, and what needed to be done for his funeral.
It was so sad, it really struck a chord with me, that story.
There is one specialist OCD in-patient clinic in the UK. The patients there are in such a bad state that they can't be filmed for a documentary. The lady there showed some of the steps she takes sufferers through to try to bring them back to reality. First she will try to encourage them to touch the knob of a toilet door, and then wipe their hands all over their face, skin and clothes, and then just be able to tolerate their conviction of dirtiness for several hours. She progresses them through the bathroom until eventually they have to wipe their hands all over the toilet seat (which is perfectly clean) and then all over themselves, taking small steps at a time to try to bring them back. Even the presenter, who suffers very mild OCD, was really reluctant to do this.
The presenter's mild OCD drives his housemates mad. He will take the ketchip and the HP sauce out of the fridge and pour dribs and drabs out of one of them until the two sauces are at the same level, and then puts them back. He won't let anyone go in his room, or even stick their head round the door, because is room is the one place in the world which is ordered by him, to his exact needs. And he is a mild case.
So when I read on this forum and elsewhere that mental illness doesn't exist...