You may be right about us civilians not being able to relate, but we still care. My son-in-law has some issues with PTSD after four deployments. He also suffers migraine headaches following being exposed to an IED explosion. He was also fortunate to be sleeping when the mess tent in Iraq was blown up, otherwise he could have died. Instead he helped with the clean up after the explosion. These are things that stay in your mind forever. Imagine seeing your buddies' body parts spewed all over the place inside that tent. Not a memory anyone wants to have nor one that is easy to forget.
^^
Caring is definitely out there, it's just hard to get someone to relate to the experience when we're trying to describe something specific like getting mortared, living for weeks in the field doing night ambushes, etc... usually the smallest stuff!!
Tell your son-in-law I had a friend who had the same migraines- he was in an L.A.V. (Armored Personnel Carrier/Stryker) when it ran over a mine, he wasn't injured but kept getting migraines... EVERY year they get less and less, and now he hasn't had any in past 4 years!