It does sound like he has some kind of head or neck pain. Maybe he has a headache and he can not tell us.
He could also have a concussion if he is not eating.
Unless it is normal for him to skin a meal.
The aspirin can upset the stomach if he does not eat with it.
To help reduce excess stomach acid, you can give him 1/4 of a human 10 mg Pepcid ac tablet when you give the aspirin.
Since he has a history of heart disease, and he is not eating, I think he should be seen by a vet.
The worst, or best depending on how you look at it, is the vet will say he just has a sprained neck, jaw, or headache. Then he will be given a pain medication that is more effective than aspirin.
I hope this helps.
If you have additional questions, please reply.