Did you overfill the oil or something? The dipstick is in the oil pan isn't it? Maybe your piston rings are done and pressure is building up in the area that the dipstick is in. It sounds like something is pressurizing due to failure of something.
My vote goes for the bad piston wrings. I think there is suppose to be some crank pressure but not much.
this happened in my 20r and it ended up being the pcv valve that was the first of three to fail on three different engines could never figure out why it did that