What Causes Indentation In Forearm After Taking Excedrin?

My son who is 25, 5 7 and 110 lbs and has cerebral palsy had a seizure this morning. He is on medication for seizures and hasn t had one in sometime. He has had a pretty bad headache since the seizure this morning. Advil doesn t seem to be helping so I gave him some excedrin just a little while ago. When I was putting him to bed I noticed an indentation in his forehead. Should I be concerned?