In drunk mood but had no alcohol - irrational behaviour

Hi,

I have posted this in a couple of the mental disorder forums, as i am not sure which one it fits into best so i appoligise. I really hope that someone can help me. Someone i know will go from being completely "normal" to acting as if they are drunk and irrational, even though they have had no alcohol. It is like a light switch and either happens over a period of minutes, or slowly happens during the day. They have had no alcohol at all but the only way i can describe it is as if they are drunk. Their behaviour completely changes and they do not know what they are doing and once they have come out of this "mood" they cannot remember very much about it, if anything at times. During this "mood" they often act depressive, feeling the world is against them, repeating themselves, and in very extreme times they slur their words and speak jibberish. They also sometimes become aggressive and nasty, not violent or anything like that, but being nasty is not in their nature at all. If they sleep it often goes away and they are fine again, but sometimes it doesn't. It often happens after they have been busy doing things.

Does anyone have any idea what this is? I have searched high and low on the internet for anyone else that suffers from this condition and cannot find any information. Is it some kind of disorder, does it have a name? I need all the information you have possible. Thank you in advance...