It could be a tension headache caused by the trip.
Often if I'm having a tense trip one side effect I get is tension manifesting itself in various ways; nausea, GI tension, muscle tension, feeling cold, tension headache.
It's not the drug causing the problem; it's a tension in your mind that the drug is amplifying and manifesting itself physically.
You could try taking an aspirin or ibuprofen. It could help but it also might not. You might find after working through the tension that it goes away.