Weird experience

Okay so the last two ultrasounds I've gotten when I lay down so they can check the baby, I don't know what happens I don't know if my uterus puts pressure on something or the baby does. But both times I laid down I've felt myself slowly blacking out my vision gets weird . I start sweating really bad, my ears start ringing and my heart races. Anyone else experiencing this? It totally freaked me out.