There's little reason to panic.
Many women experience what is called orthostatic hypotension or prostural hypotension.
When people lay down, the body does not have to work as hard against gravity to pump blood all over the body. As a consequence, blood pressure lowers. Suddenly standing up requires the body to activate a number of heart and blood vessel responses to raise the blood pressure to the levels that a standing person requires. If the response lags, there will actually be a drop in blood pressure and this results in an inadequate blood supply to the brain. Therefore, a person with orthostatic hypotension may experience dizziness, changes in vision, and an uncomfortable feeling in the head and neck area upon rising from a lying or sitting position.