You probably had it in reverse for no more than a fraction of a second. The fright must have made it seem like a full 4 seconds. Really, look at your watch and see how much time 4 seconds really is.

If it is an automatic I would not worry as much. The other guys are right, you should change your auto tranny fluid soon.

The way the auto tranny works is you have a "propeller" spinning inside a "sticky" fluid that has the interesting property that when it heats up, it solidifies. When the propeller spins, it heats up the fluid... when the fluid heats up it "locks" up the movement of the propeller to the wheels. If you toss it into reverse it would certainly impart an extremely large amount of heat into the fluid. If you really did have it in reverse for 4 seconds, that would be a problem. But I suspect you only had it for a fraction of a second, came to a sinking feeling in a fraction of a second and got out.

Calvin