Although everything stated so far is fairly accurate and will negatively affect steering, they don't explain the sudden appearance of the problem. I have had this happen on more than one old CJ, and every time it was due to a bad tie rod. I bet you either hit something that bent it or, more likely, the adjusting sleeve is slipping. Years plus bigger tires plus rust can cause the tierod to get pulled out, like with the force of a turn lyou described. Then when you try to return the wheel to 'straight', one of the tires is actually off at a slight angle. Then you force the steering more to correct, sometimes it slips back in place...but eventually the rod ends up bending under the force. I would check your rod, sleeve and ends before anything else.