I often go to sleep at 4-5 AM. Do I say hamapil then? What about someone who has a night shift – if he goes to sleep at 8:00 AM every morning, does he say krias shema al hamita then?
If I know that I will be going to sleep that night and that it will be very late (say, 4-5 am), I usually say HaMapil around 1-2 am to guarantee that I don’t accidentally fall asleep without it.
Someone who is up all night is a Machlokes HaPoskim. I think the Tzitz Eliezer or R’ Ovadia has a Tshuvah where he brings down the relevant sources.
MA: I am aware that it is a Machlokes HaPoskim and that Pashut Pshat in the Sugya is that it’s perfectly Muttar (certainly for Ashkenazim). Therefore, in a Bedieved situation, it is better to make sure to say the Bracha (and not risk falling asleep without it) than to not talk after saying the Bracha.