I have a wonderful friend whos bi-polar,he has it under control with medication,however?

hes recently had an episode where hes confused me,one minute he was elated and joking with me,a few hours later he got kind of snappy,since i dont know bi polar workings i was taken by surprise,i thought it was a brushoff on his part.i know this is a mental illness,can anything be done sos i can help him?