My husband was in 2 car accidents within 3 weeks
may not be related to head injury...
Based on the details provided, the two accidents were about 18 months ago. Yes, immediately following head injury, swelling and concussion are expected. But these changes resolve over a period of time. And 18 months is more than enough time for resolution of any swelling or concussion that could have occurred. Unless he had a fairly large bleed and brain damage he should be neurologically fine.
But since he has aforementioned symptoms, I don't think they are related to past head injuries. Perhaps the symptoms are related to chronic headaches (migraine) and or somatic disorder.
Hope this helps. Let me know if you nave any other specific questions.
Abnormal body response...
In simple terms somatic disorder refers to a condition where the body responds involuntarily with wide variety of symptoms in response to a triggering factor. The triggering factor in most cases is stressors. It is a mind related condition and there are no other physical causes to explain those symptoms. Neuropsychiatrist or a psychiatrist will know about it and can treat you. In my opinion you should consider consulting them if you haven't seen one yet.
Hope this is clear. Let me know if you need clarifications.