Sexual fantasies that I fall asleep to are often simply getting into a warm bed with heavy blankets with two pretty girls, maybe 18-22 years old. One is in footed pajamas (one-piece, pink, green, or ABDL-patterned fleece, with the zipper going from neck to one of the attached booties. The booties are attached at the cuff and have white vinyl soles and toecaps). The other is in a frilly, white or green nightgown with (if white) pink, red, or blue accents (think Clara at the Nutcracker) and with a big bow in the hair, and white tights and satin booties. I'm lying “middle spoon” even if the girl in back is shorter. Both girls are wearing their masks, which could be N95's (or equivalent), P100 cartridge respirators, or even cloth masks that have either two headbands or two ties done in bows.
If I'm in the shower rather than getting in bed, my fantasy involves receiving a tight, messy tongue-swirl blowjob that severely violates her gag reflex. In the fantasy, she and I might be in the shower as I would be IRL (so the mess would go down the drain), or I may be laying on my back on my bed with her kneeling, spitting on my penis and then performing the blow job.
In the first fantasy, there aren't any particular girls joining me in bed, but invariably they are cute vs. sexy. In the fellatio fantasy, it is either a 5ft 6 19/f brunette that I once knew, rather thin, or two twin sisters about that same age with dirty blonde hair, green dresses, green tie-on fabric masks, white tights and black ballet character shoes. I didn't know these two but saw them at the Nutcracker in December. Obviously whoever is doing the blowjob takes off her mask, leaving it hanging on her neck.
If the OP is talking about dreams that happen in deep sleep, for a year or two I was able to remember my dreams clearly, which I liked. I remember always feeling refreshed, even if the dreams were pretty weird. My dreams during this phase where never nightmares, but just kind of resembled mundane reality, but with a twist that would never occur in real life. Like taking a transit bus but winding up several hundred miles away in Albuquerque inside a busy bingo hall rather than the bus stop at Main and Division in my home city. Maybe the background music of the dream is the William Tell Overture at ½ speed with Tupac supplying the lyrics to this IRL instrumental.