Sounds like PVCs or PACs. But if you are afraid, you should visit a doctor and get an EKG registered when you stand up, so you know for sure what this is and isn't.
That said, the heart can speed up or initially slow down when standing up, that's fairly normal. I think you can relax, you are not going to die. Even if you did have a short run of NSVT (which is very unlikely), you are not going to die.
If you feel at risk tonight, go to the ER. Or call your doctor first thing in the morning. At the very least you will have peace of mind. Better safe than sorry.