For the record, I don't think such a disorder exists...but I'm pretty sure I suffer from it.
Every night at bedtime I take Isaiah to his room and tuck him into his bed. (You can read more about that adventure here.) Once he's asleep I leave the room.
Mysterious happenings go down after I leave the room. I'm not exactly sure what, but something happens. Because every morning I'm awakened by a wiggly bundle of Isaiah squirming around next to me.
First I double check that I am, in fact, still in my bed. Yep, didn't wake up in the middle of the night and opt to go sleep on a lumpy, bumpy, old twin bed with a teeny tiny toddler blanket.
Then I frantically try to replay the night in my head. OK, I put Isaiah to bed at 9. Went out,
wasted time on pinterest cleaned the kitchen. Brushed my teeth. Went to (my) bed. Isaiah woke up as soon as I shut my eyes, of course. I went in and got him back to sleep and ninja hopped my way out of the room so he wouldn't notice any changes in air movement and wake up again. Tucked myself back into bed and went to sleep.
Hmm, I seem to be missing something in my mental replay. I don't remember hearing him wake up. I don't remember going into his room again. I don't remember him coming into our room. Yet, here he is.
I text my husband (or just ask if he's home) to see if he heard him wake up and tended to him during the night. Nope, he has no clue how the child ended up in our bed.
Now either the child has super sneaky, feather light abilities and can wake up, stumble into our room, climb up the bed, slip himself in between my husband and I and get himself back to sleep without ever bumping or waking us OR (and probably the more realistic explanation) I do things during the night and have no recollection of these actions come morning. Thus inventing and self diagnosing myself with Nighttime Amnesia.