Apples stimulate the release of bile along with liver toxins.

I would experiment and take Algin 6 hours and then 3 hours before eating an apple and see if the effect is minimized. If so, the headache may be the effect of reabsorbed heavy metals in the intestines.

This type of headache could also be caused by a simple sugar low. Try taking GTF Chromium 30 minutes before eating an apple and see if the effect is minimized. If so, this may indicate a hyper-insulin condition. (Don't use chromium picolinate. It is useless for most people.)