Classic sign of a paleo not drinking enough water. We tend to forget to drink water because we are seldom hungry. We just don't get the thirsty pangs. As posted elsewhere take your weight in pounds, divide by two, and take that number in ounces as a good rule of thumb for water intake. I add about 25% to my number. I have to constantly remind myself to drink water.

I used to sometimes feel like this and thought it was classic signs of low blood sugar. Then I got a glucometer and found out my blood sugar was totally perfect the whole time and not low at all. And the problem went away by itself over time. My advice is check your blood sugar before assuming it might be good for you to stuff down a bunch of sugar.
-Eva

try something salty

I have blood sugar that barely moves up when exposed to sugar or high glycemic food but then plummets. I therefore avoid those and eat every 2-3 hours to prevent dips in blood sugar. I eat protein and hardly any carbs. If my blood sugar is low I eat protein not sugar because that is my understanding if you have hypoglycemia. Of course this is different from those who have high blood sugars that swing with lower levels.

My first day trying to go completely paleo, I ate a sweet potato, and a couple hours later I had a blood sugar crash. I was near my organic market & pulled in for an emergency supply of gluten-free cookies. It stopped the cold sweats & brain fog, but now I have to get back on the sugar-free wagon... again. I felt sooo good until the crash. Now my brain hurts. Maybe next time I'll be near my meter, or I'll go for the protein or water or salt instead. I'm kind of afraid to go completely paleo again.