My 6-year-old was nauseous so i gave him the recommended dose of dramamine/dimenhydrinate for his age (25 mg), and he began seeing things that weren't there. once the medication wore off, he was back to normal. is this concerning?

It is a side effect worth noting as it is likely to happen anytime it is used. Beyond that it just reflects a known reality that this drug penetrates & works on the central nervous system to combat nausea.

The occurrence may be related to the medication. Ensure no medications are missing at home, and that there were no drug interactions. A viral illness also may cause the symptoms. Encourage small sips of fluids, dry crackers and toast until well. Poison control should be contacted if recurs. Watch for signs of vomiting, headache and fever.