Sounds like a sacked or broken spring. A quick look underneath will reveal if it is broken. If it's not broken, make your way underneath and compare the loaded height of each spring. If it is worn joints, I wouldn't think you would have this much height difference from one side to the other, but give everything a look over. If the springs seem okay, raise the car safely and do the "4 P's" on all suspension joints. Push, Pull, Pry and Prod.

Hope this helps