No, I have absolutely no idea why, unfortunately. I do believe the dreaming aspect is quite normal though, but it seems the falling back to sleep and anxiety is the issue for you? Maybe try some nice relaxing teas before bed or listening to recordings of relaxing sounds, perhaps meditation too, things like that, and see if it helps you stay asleep during the dream phase.

Psych Central has some good resources too, so I wonder if you'll find something helpful here: Sleep Disorders & Insomnia Guide | Psych Central

It's all about sleep and related questions.