• Odd causes of headaches:
  1. celiac disease (GSE)
  2. temporal arteritis [LMC-03-5788]
  3. rebound headache (those who have regularly used aspirin, acetaminophen, and other pain meds for headache may get dull...often morning...headaches because their systems "want" some more drug. Lack of caffeine in a caffeine user can do the same).
  4. "shingles" (herpes zoster...VZV) with or without definite skin rash.
• Migraine headaches: these become throbbing and and can manifest as temporary blind spots, loss of balance, or abdominal pain.
• Tension headaches: Your headache primarily occurs in your forehead, temples or the back of your head and/or neck...continuous & not throbbing.
• Hypertension headaches:
• Brain tumor headaches:
  • cerebral tumors:
  • posterior compartment tumors
  • pituitary tumors: usually frontal or facial but can trigger "vascular type" headaches
• Other:

References:

1. National Headache Foundation website has much info.