Four days with a migraine is the longest I have gone. Even if I put a spoonful of water in my mouth I'd puke. That was back when they would give you opiates to break the migraine, they don't work as painkillers for it but make you high enough to finally sleep - pain felt so far away - and I would wake up with no headache. It's happened about 7 times total in my life, now they won't do that but they do IV fluids to prevent damage and some antihistamine to make you sleep but it doesn't break the migraine. Hopefully it never happens again.
On purpose I have fasted 3 days but would NEVER purposely fast without water. Water with electrolytes if going more than a day or so.