the dimmer switch is going out if you are experencing that.
Low beams are burned out.
The headlights are on two different fuses. The high beams are on one fuse and the low beams are on another fuse. The fuse for the low beams may need to be changed.
Check the fuses.
Your headlights may not dim because you don't have dimmer lights. Dimmer lights can blow and leave you with just the high beams.
Because the lights are so bright
I would first check all fuses. My 2002 uses a weird configuration and requires several fuses to work all of the lights properly.
Your headlights are operated by twisting the end of your turn signal stalk. One forward rotational click, from the off position, turns your running/parking lights on. The next click turns your running/parking and your head lights on. The third click is "auto". In this positions your lights will turn on and off automatically depending on how much ambient light your vehicle is in while driving. Pushing the turn signal stalk forward turns your high beams on. Pulling it back again turns the high beams off. Your daytime running lights stay on whenever the car is running.
Using low beam headlights and front facing fog lights.
Parking Lights or low Beams.
If by "dim headlights" you mean low-beams... the bulbs are bad and must be replaced.
Check all fuses and check for burn out headlights, high and low beams
I think faulty light switch.