Is throwing up a sign of dehydration, what's the proper way to rehydrate without getting sick?

Not sign: Persistent throwing up can cause dehydration, but it's not a sign/symptom of it. If taking fluids is making you throw up, proper rehydration is as follows: First, let stomach rest for about 2 hours where you don't try to take anything in. Then use a rehydration solution such as Pediatlye or low sugar Gatorade and take just a teaspoon. If you keep that down for 5 minutes, take another teaspoon.