I've had a few over the years, albeit not too frequently, thankfully.
The one I've had several times as an adult has been waking up utterly convinced that there's a giant fly/wasp/insect (delete as appropriate) in my bedroom. On each occasion i'll wake up and jump out of bed in one motion and either run straight out of the room, or to a far corner, heart beating through my chest. Once, several years ago now, this happened and it was a wasp right above me on my light shade. The wasp was the size of my head. I shot up and out of my bedroom and slammed the door behind me and stood there with my back to the door. My bedroom was next to my roommate there and he heard me slam the door and came out to see what was happening. It was only when he started talking that I realised it was *probably* just a dream, and I said I was all good, before slowly edging my way back in. I still checked under the bed and shook the covers out before I got back into bed, mind.
On triggers, I guess it kinda goes without saying that I'm not a fan of insects of any description, really, and on the wasp occasion, I'd had a wasp nest discovered just outside my bedroom window there and one day I came home from work and found the window sill and bedroom floor alive with them. Doesn't take a lot to trace that correlation. No idea why the fly variation came from, mind you.
The thing with these dreams is they're so unbelieveably vivid and they seem so real at the time. I've had these dreams a couple of times while I've been with my wife. First time she wondered what the hell was going on as I climbed over her in the middle of the night to get away from said fly.
Anyway, not happened for a while now.