I think it may be different for each individual as i have the diagnosis of schizo affective disorder, but for me though it's psychosis that trigger's off mood episode's and in recent time's i've had no happy mania it's a mixture of depression / mixed rapid cycling as i believe it to be fueled by extreme paranoia and Hallucination's .
I think mania is more dangerous aside from suicide. I confronted the Guatemalan military in '89, the end of their civil war. Middle of nowhere 12 hrs down a dirt road is an easy place to disappear. I slept in the streets of Bangkok and the prostitutes and homeless feared for my life, but I didn't. In depression catatonia is the worst that I felt. I am not a suicidal person, but I have wished I was never born. I've missed work, blown off people and isolated when depressed, but my instinct tells me in mania, "Get a plane, hop a train to get to the airport, hitchhike to the place trains slow down." So, for me, mania is more dangerous, but fun sometimes, while depression is so horrible, but afterwards, life hasn't change very much. I do think depression kindles though. Damage is done from severe depression that I think accumulates similar to mania. Depression does seem harder to cure in many cases. Depression is the worlds most common disorder, all over the world people suffer with no other explanation than neurochemistry. Good question.
My answer, mixed is the most torturous and is the most dangerous for me. I can get VERY depressed and still understand that it is an illness and do things that help or just understand that I will have to ride it out. I know it will end because I have had so many depressive episodes and I came out every time. I know what meds work, which make it worse and have a good relationship with my doctor. Mania is similar. I can get fairly high and understand that I am high. I know it isn't a bad time to be shopping, and it's a good time to be rigid with my daily routine. I know to call if I have insomnia for more than a few nights. The trick is not slipping into psychosis before doing something to stop the mania. I think the repercussions of mania are worse and can cause a depression on all in its own.
For me, a mixed episode is not sleeping with intrusive, disturbing thoughts along a sense of exhilaration. The incompatibility of the two is impossible to live with and I end up incessant horrible thoughts. I sleep, can't focus on any thing and that is when my risk of suicide is highest. I need rest, I need my brain to STOP torturing me, whatever did I do to it to do this to me? And I can't talk to anyone about it. I just spew out cryptic stuff, not because I'm psychotic (yet), but because I can't tell you what thoughts are going through my mind, it's too embarrassing and bizarre.
It starts out small, but I recognize it and I know, hospital time is coming. What embarrassing things am I going to say and do this time? So I try to hide it. Never works out well for me.