My cat is over grooming and has changed her old habits. She has had fleas when the personality changed, they were quite bad as I had not noticed, they have now been treated. She always slept on my bed, but now she will not even come in the room. If I take her in there she cannot get out quick enough, this has now progressed and she will not even come upstairs she appers frightened, she stops purring and runs down quickly when I put her down. She does drink more then she used to, I have put this down to all the extra grooming she does, especially her rear end and tail. She is 11 year old and I have had her from a kitten

How long has this been going on?
I would take her to the vet for a general check up.

Could be worms, so a vet check would be best. Usually when an animals has fleas it goes hand and hand with worms.
Sometimes you can go to your regualr vet, and tell them you want a flea and worm medication they can prescribe with out seeing your cat. Although taking him to the vet would be the best idea.