late addition to this old-ish thread, but I was interested because i literally have the nightmare of spiders descending upon me from the ceiling a few times a week. It's the exact same nightmare every time. It's terrifying, though fleeting. And because of so much experience and frequency, my brain recognizes it fairly quickly and i'm able to maintain my composure and just wait for the imagery to pass. Suffice to say the first few times the nightmare occurred, i screamed and dove off my bed for cover.