If you are pregnant and have any questions at all you pick up the phone. If you aren't pregnant you can wait a little longer. But if you are pregnant, you don't want to be waiting around for your skin to stop snapping back.
When you can't keep anything down, you're dizzy/light headed, and if you pinch your skin and it doesn't snap back into place. There was a certain spot and I can't remember where, I think the wrist.
Also, if you have gone 24 hours without being able to keep anything down. There are other signs but I can't recall them all.