"Debilitating headaches" refer to extremely severe and incapacitating head pain that significantly hampers a person's ability to function normally. Full definition
I have been struggling with debilitating headaches all my adult life. (greensmoothiegirl.com)
A study has shown temperature rises increase the number of people requiring hospital treatment for debilitating headaches. (climatechangepredictions.org)
Diagnosed with a concussion, she returned a month later, but was injured again, the crushing blindside hit causing a concussion so serious that, as she later posted on her Facebook page, she was left her unable «to read, remember, think clearly, go outside without dark glasses, or stand for 5 minutes without debilitating headaches, dizziness, and crippling fatigue.» (MomsTeam.com)