When playing with modified health in minecraft you have the chance to encounter a fake death screen, i managed to reproduce this bug pretty consistent by modifying the health to 200 instead of the default 20.
What is happening when you have more or less than 10 hearts and are on full health, and somehow you die or your health changes again and get a damage tick or a regeneration tick you have a chance to get a fake death screen, this can be an issue in pvp or mini games that use custom health.

See this Video for a better idea for what i am talking about.
https://www.youtube.com/watch?v=Ziq7gG4KQvQ

just a quick note, the iron blocks in that video apply a instand health 200-ish to instantly heal anny amount of health, so the bug can be shown faster