You may have constrained some blood to your head.If you feel uneasy laying down, you should tell your dentist. After all there they're so your comfortable.
If you happen to freak out, (while filling cavities) or something, and your burst up out of the chair, the dentist could drill a nice hole through your teeth and into your gum.
If you feel uneasy give your dentist fair warning.
need to make sure you eat before you go into the chair... sometime the anesthesia can bother some people... the most common i have heard is when your sitting for a while, once you get up alot of people(including me) get dizzy and feel faint, that is due to the blodd rushing back into your arms and legs, causes a drop in blood pressure..... have you told your dentist that you start to feel sick?....please DO NOT let them keep working on your if you feel this way, it could end up badly and you in the hospital ( if you faint or whatever happens)