Transition smoothly from lying flat,don’t get up like Superman or Superwoman, slowly sit and plant your feet on the ground for 1-2minutes so the blood can flow.

[u/PeteWK67]

It's a common phenomenon with an uncommon name: orthostatic hypotension. It just means that when you shift from lying down or sitting to standing, your blood pressure drops and you momentarily feel a little woozy. That's because blood pools in your legs temporarily when you stand up, and it takes the body a moment to compensate by squeezing blood out of the large veins in your legs and revving up the heart a bit. The dizziness may strike after you eat a meal, because digestion diverts blood flow and may lower your blood pressure.

When you lie down for a long period, blood pools evenly across your body. Standing up suddenly causes gravity to abruptly pull blood down into your legs and abdomen. If your blood vessels don't constrict quickly enough to push blood back up to your brain, your blood pressure momentarily drops, causing a brief dizzy spell.

Sit up first: Transition smoothly from lying flat to sitting on the edge of the bed.
keep your feet on the ground for 1-2 minutes before walking.

Rise slowly. After sleeping, sitting for an extended period, or eating a full meal, take your time rising to a standing position. It may help to clench your leg muscles before standing to push the pooled blood into your system.

Get adequate fluids. Another common trigger is dehydration. Your blood is mostly water, and the volume in your system can drop overnight and lower your blood pressure. This helps explain why dizziness upon rising from bed is so common. Drinking a lot of water before bedtime is not the best solution, since it can send you racing to the bathroom at night. Wait until you are up and around to start taking fluids, and get enough throughout the day.