noun
just after falling asleep; the moment one falls asleep
Refers to the shallow sleep stage right after dozing off, often used when someone is easily woken or disturbed.
寝入りばなに電話がかかってきて、起こされた。
I was woken up by a phone call just after I had fallen asleep.
寝入りばなは夢を見やすいと言われている。
It's said that you tend to dream easily just after falling asleep.
The verb meaning 'to fall asleep'; 寝入りばな is the noun form referring to the moment right after that action.
Compound of 寝入り (falling asleep) + ばな (just after, from 端 meaning 'edge' or 'beginning').