I figured out what it was when I went on a journey and left my electric toothbrush at home. After a couple of days the headache was gone, but when I got home and started to use the electric toothbrush again it soon reappeared.
Now I only use the (in regards to dental hygiene, superior) electric toothbrush a few times each week and the headache stays away.
It's no funny thought, but I wonder if one could sustain brain damage if exposed to the vibrations of electric toothbrushes too often.
The reason why I started to use an electric toothbrush was that hard toothbrushes disappeared from the market a few years ago, and hard toothbrushes were the only means I knew of which effectively kept tartar off my teeth. For a while I even used a kind of toothbrushes meant to clean prosthetics (brushes which were hard enough to clean the ownen with) before I discovered that electric toothbrushes were just as good, or even better, at cleaning the teeth.
The reason that hard toothbrushes are removed from most markets was that some people damaged their gum with them, causing gingival recession, which in turn caused hypersensitivity and in worst cases loss of teeth. That brushing alone should count for loss of enamel or cementum though, is a myth.
I've never experienced such problems, nor cavities and similar either, despite that I used hard toothbrushes for more than 15 years, and the reason for that is how I brush my teeth.
If you wish to be spared from hypersensitivity in your teeth then the angle you hold your toothbrush is the most important thing to keep in mind; you should brush your teeth "with the fur" and never hold the brush so that the bristles can tear into the gum. You shouldn't either brush your teeth more than twice a day, do instead complement with fluoride rinse and xylitol chewing gum.
That's it, no cavities and no more hypersensitivity - it's (usually) as easy as that.
Brush in this manner and sensitive teeth comes with a guarantee.
The gum gets weared and the dentin (dentin is a mineralized connective tissue which makes up most of the tooth's root) becomes exposed, and the nerves within reacts so that you feel a shooting pain, especially when you consume cold and acidic stuff.
If you brush this way you will probably not experience sensitive teeth.
After a while you can chew popsicles just as when you were a kid (and all the grown-ups got the shivers when seeing you doing it).
Sensitive teeth gel or sensitivity protection toothpaste is as you can see no cure, but can help during the time the gum is healing. Pain-relieving toothpaste could actually worsen the situation if you continue to brush your teeth in a wrongful manner, since you won't notice the damage done as much as you should have done without the pain-killer.