I think dreams normally last only a few moments whether frightening or not, and however long their invented narratives are supposed to last. The nightmares are more vivid, and more likely to be remembered, though.
Usually we forget dreams very rapidly unless we make a deliberate effort to recall them, and often do not even realise we had been dreaming.
I used to be prone to quite dangerous nightmares, but thinking back, I realised I could re-play them by memory within only a few seconds even if the scene itself would have taken a lot longer in reality. Though most were too absurd to have happened in real life.
Dreams compress their events and times to rapid summaries of the main points. From remembered dreams it appears we can "jump" from one location to the next in the "bed-time story" our mind has concocted, ignoring the intervening travel method and time.
Bit like a trailer for a TV drama or sports event maybe - squashing a lot of narrative into tiny but significant points lasting only seconds, or less.
"Dangerous" as in "life-threatening"? Then going to sleep would not be a favorite thing not knowing what awaited you. Did you sleepwalk perchance? Of course you don't have to answer that. Some "dreams" are really funny odd bizarre peculiar. There are people in them with all kinds of strange but very docile pleasant non-threatening behaviors. They speak nonsense but in the dream it makes perfect sense. Sometimes I recognize snippets here and there of dialogue or situations I've seen on TV or elsewhere. Once in a very very very great while I know I am dreaming but it is so rare. I read that if you don't dream you will go mad. Or maybe the mad don't dream? I know sometimes I go to sleep having problems I didn't solve and wake up with the solutions so maybe it's a place to figure things out? Thank you for your reply Durdle! :)
If not quite life-threatening then certainly risking serious injury by falling down-stairs or as I have stopped myself doing once or twice, from the bedroom window. I don't remember ever sleep-walking though.
Most of my dreams though are amiable nonsense, though over the last year have more often referred to all the social things I am missing.
I think the sort of dream you are conscious of having is called a "waking dream". They are common generally, but not necessarily to the individual. I have tem sometimes, but they are very, very short, fleeting moments.
I don't know if that's true or not, about going "mad" if you don't dream, but there might be disorders that stop you dreaming. I think we dream a lot more than we think, but some people don't remember doing so. Solving a problem while you sleep is unusual but I gather you are in illustrious company if it happens.
Sleep is a complicated thing and is known to be necessary, though I don't think it's fully understood yet. One thing that is known, is that during sleep the brain is busy with its house-keeping (as is most of the rest of the body), and seems to need us asleep so we're out from under its feet while it's busy.
Durdle 