Is it possible to start having bad symptoms after being home for several years after serving in combat?
Yes it is possible and it is very common. Post Traumatic Stress Disorder (PTSD) can show up many years after the actual combat stress occurred. And the symptoms can be just as vivid as if you had just experienced the trauma yesterday. This could include nightmares, flashbacks, anxiety, agitation and nervousness, difficulty thinking clearly, depression and feelings of being in danger.
There are effective treatments for this. My first choice of treatments would be EFT. In my experience, EFT is one of the fastest methods to eliminate PTSD symptoms permanently.