Hia,
I know my NM dentist says you can't overtens, but I disagree. Each person is different and I know from experience that I have felt very bad from overtensing.
First of all, there can be a build of lactic acid and toxins that are released when you tens, especially so when you first start tensing. When your body isn't used to this, you may react. My NM dentist did give me a head up on this one. He said to drink tons of water before and after tensing at his office, or at home.
Also, certain people are highly sensitive to pain/treatments/stimulus. I am one of them... For example, even the gentlest massage makes my TMJ symptoms worse. When you have a moment, research the term "central sensitization". If this applies to you, as it does to me, you could react to tensing. At a regular setting, the machine may be too high for you and may be on too long for you.
Hope that helps.
All the best in your recovery,
Melissa