I sometimes get into a state of bliss quite randomly, then "crash" and feel all sad-like. what could cause this? i'm on fluoxetine and benzodiazepines

Dangerous: This sounds serious.You must see your treating physician and tell what's happening to you.

Discuss with doctor: The doctor who prescribed your medications is probably a good start for considering possible changes or tapering off. I'm imagining by random - that it isn't a reaction to what's going on around you, but rather inside you. Does it have a time pattern connected to your pills? If you can find a good psychologist to talk about issues with, you might not even need them. Best wishes.