Regardless of how much more empathic or insightful a chronic illness has made you, I don't feel it should be brought up on these applications unless you can assure programs that it is under control or in remission that is reasonably expected to be maintained, that you're under the care to keep it that way, and that if it unexpectedly returns you now have the experience to recognize the early symptoms and get help before it impacts your performance.
The natural course of migraines, chronic pain, and PTSD is that they can be severely debilitating, sensitive to changes in stress/environment, and remain in many cases unpredictable even after periods of good control. They go against everything that an adcom would want to hear to feel confident you could succeed in the rigorous environment of medical/dental school. PTSD aside, migraine and chronic pain are intimately intertwined with mental health, and there are plenty of threads about the stigma of mental illness in gaining admissions.
I would not mention these things at all unless you want to raise suspicions that you'll be a student who can't handle the physical or emotional stress of your professional education.
