IBS does not physically get worse with time, but it may get harder to deal with over time, but IBS itself does not progress into anything.
What was the treatment you were on for the IBS?
Have you been to a doctor recently about this?
Stress can make IBS worse for sure and it can come and go or wax and wane. Foods can also trigger something called the gastro colonic responce, which is why you can have symptoms so fast. It can be from the "act of eating." Some foods can be problematic as well, but foods and stress don't cause IBS, but can make it worse, especially stressors, both physical and mental.
Sorry to hear you were in a car wreck.