Night Vision flickering

If you use or give yourself a unlimited night vision potion, after a long time using it, it will first flicker slowly like a night vision would end, but after a short time (feels like 5 seconds or so) it starts flickering very fast.

I din't found a other thread wich descriptes the same, so.... here it is!

*open both images in tabs and switch through them, so you see better what I mean.*