Very interesting.

I often wake up at night or early in the morning to go to bathroom, or take water. I found that the best way to go back to sleep after waking up is to think about the dream I just had. It seems like this 'forced' dream continuity is somehow sleep inducing.

What may be happening to you is the same thing: your firs instinct is trying to remember your dream, as you trained yourself through years of dream journaling. It's a learned behaviour. But what happens is, this induces sleep, and you're caught in the loop.

Maybe the trick is to go back to writing down your dreams when you wake up. This activity may keep you from falling back asleep.

Hope this helps.