I dont think its abnormal at all, i think its perfectly normal.
I would say more people have done this sort of thing, they just dont admit it, bipolar or non bipolar.
My best friend once found a guy on a site, went round his house, slept with him and then came back.
Risky behaviour is a symptom of bipolar but isnt exclusively so.
However i understand how crap it can make you feel the day after. You get the adrenaline rush from doing something you shouldnt then the come down from feeling ashamed of yourself.
I go six months without sex and then six months where i'll go with any randomer and am obsessed by sex, its not even dependant on episodes.
I was once in a mixed episode, laid in bed, thinking about sex, i got up, locked everything valuable in me and my friends house in a cupboard (very paranoid at the time, yet rightly so considering what i did) went out, found four guys leaving a night club, practically forced them back to my house and slept with two of them, as soon as i finished i kicked three of them out, but one passed out in my bed so i locked myself in the spare room all night until he was gone, cause i got my kicks and just looking at him after made me feel sick.