I am newly diagnosed with SVTS. Are headaches a common symptom?

They can be. I never....ever....get headaches, and didn't when I was in flutter, having PACs, or in atrial fibrillation. But each patient is a unique animal when it comes to drugs, alone or in combination, and to various disorders and diseases. So..yup:
https://www.healthline.com/health/causes-and-treatments-for-heart-palpitations-alongside-a-headache
Not that you'll be happy about it, but welcome to the 'club' of arrhythmias.

I discovered that dehydration can be the cause of headaches and heart beat problems. I never drank hardly any water. After reading that, I am forcing myself to drink water, still not up to 8 glasses, but the difference is obvious. No headaches and a GREAT decrease in afib or whatever. I began Jan 1st.

Good catch. I, too, suspect dehydration is a contributing factor to my episodes of a-fib. I generally have no sensation of thirst until bedtime, so I forget to drink. Now I'm trying to pay more attention to my fluid intake through the day. As a nurse, I'll point out what may not be obvious to everyone: fluid intake is comprised of all liquids, not just water. When your fluid intake is being recorded in the hospital, the total will consist of "clear" liquids that are mostly water (coffee, tea, juice, soda, jello, broth etc.) and "full" liquids with high water content (milk, pudding, creamed soups, ice cream etc.). So if you aren't a big water fan, you can meet your body's needs for water in other ways.

Coffee and tea is NOT good for Afib. Neither are sodas with caffeine, which includes Mountain Dew which has more caffeine than colas. Jello is mainly sugar and water, ice cream high sugar. Sodas???

I was simply categorizing items that count as fluids/water.