This is hard to replicate but bear with me - multiple people have experienced this
When in the nether or end, you will occasionally be teleported to the "overworld" against your will
However despite the fact that the sky appears as if it's the overworld, your coordinates have not changed, no blocks will display, and all models and mobs will still interract with you (including trying to kill you)
To replicate - just hang out in any other dimension while fixing bugs for 20 mins and you will see this happen