alright first things first - check with your doctor.
with that out of the way, this sounds exactly like an exertion headache. these are usually caused by a tense muscle in the neck that will radiate pain up into your head. however, in my case, these were severly exacerbated by going VLC. it was a problem that didn't surface for months, but cleared up as soon as i dropped the ketosis bullshit. YMMV, but doing strenuous exercise without carbs works for a very slim minority of people.
"dean ornish and dr. davis think the palmitic acid our bodies use for fuel while we sleep is poison if we eat it. zero-carbers like charles washington think the oldest fuel in our evolutionary history – glucose - used by organisms a billion years ago and without which the brains of modern mammals cannot survive for more than a few minutes – is an unnatural toxin if you eat it. both views ignore basic facts of medical physiology and defy evolutionary history." - kurt harris