I'm kind of confused. Did he get back in his own body or did he lose his memory and get ba...

Jehee regressed, that's why we are back at the scene where the manhwa started. This is also the reason seonwoo doesn't remember anything.

My guess is that he was in that "afterlife" state for a really short time, and similarly to life passing by our eyes when we die, he saw the other seonwoo's life instead of his own. Maybe because they are techically the same person just in different universes?? The clock on his wrist started ticking backwards due to jehee activating his regression.