For anyone who may have (or will) experience this problem (coital cephalgia), it was definitely the magnesium. As the excess Mg left my body over a period of days, so too did the stabbing brain pains. Thank God I am now back to normal. No more Mg for me! Hubby-induced sparkliness is far better than magnesium-induced sparkliness. What a weird (and worrisome) side effect!!