Entering every single world whether created or not, no matter which version played, causes constant lag

I am trying to play on a world of mine like I normally do in this version, but more apparently than not, something very mysterious in whatever world I'm on is causing nothing more but a severely constant amount of lag from 1 (min) - 3 (max) fps, no matter how I control the framerate or something else. Very unsure why, of course.