Is my turtle sane?

Two or three weeks ago I received a Red Ear Slider Turtle from my girlfriend’s friend’s ex. One of my friends has a turtle of the same kind is pretty mellow. It completely ignores people looking at it and just floats around. Not mine. Whenever he sees someone enter the room he madly splashes at the edge of the tank trying to swim to them. Everyone I know thinks hes psycho.

And I’ve also noticed lately he’s been spending a lot more time on his rock. Normally this wouldn’t be a problem, but he is a water turtle and he’s sent the better part of three days on his rock basking in the heat lamp. Shouldn’t he be spending more time in the water?