system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What is a migraine, compared to a what one normally thinks of as a headache?
gpt
A migraine is a neurological condition.  One of its most obvious and common symptoms is a headache, normally servere.  However, a migraine is not a headache and migraines don't have to have a headache to be a migraine.  

What causes them is not well understood.