I still start dreaming as soon as I fall asleep at times. Not to do with any other things going on. Falling asleep into a dream is abnormal. I'm glad I don't do it a lot these days. For a few years as an adult I always went straight into dreaming. Actually almost any time I was awoken (by a sound, the phone etc) I woke from a dream. It was quite exhausting. It was like being awake around the clock.
I hear you're supposed to sleep soundly for 90 minutes before you start dreaming. I actually think I do that most nights nowadays.
I think hypnic jerks are so common so they don't really count as anything. But I can see if they happen much more often with people who have hypnagogic states because their sleep switch seems a bit off. I would think it is much more common having hypnic jerks going into deep sleep compared to REM sleep.
That said, people can have non REM dreams. My friend has those, she almost lacks REM sleep (confirmed) and rarely dreams but when she does, it is often non REM dreams. REM dreams are wild and crazy and full of actions. When I ask her what she dreamt she goes like "I dreamt there was a glass of milk". I ask what happened with it because in a REM dream something would happen to it. She goes "Nothing happened, it was there, that is all." She also dreamt really exciting things like that it had snowed, that there was a shoe on the floor and that she was lying in bed. All separate dreams. LOL.