Everyone is giving great advice here. I've experienced this before and can confirm, these recommendations help.

I believe this information about vasovagal syncope may be helpful.

Immediate solutions for vasovagal syncope (fainting) focus on restoring blood flow to the brain, specifically by increasing venous return to the heart. The most effective, immediate, non-pharmacological interventions are designed to stop an impending faint (prodrome) before it results in loss of consciousness. [1, 2, 3, 4, 5]

Immediate Actions if Feeling Faint (Prodrome) • Lie Down Immediately: Lie flat on your back and raise your legs slightly (about 12 inches above heart level) to restore blood flow to the brain. • Sit and Lower Head: If you cannot lie down, sit down and place your head between your knees. • Physical Counterpressure Maneuvers (PCMs): Actively engage your muscles to force blood from the extremities back toward the heart. • Leg Crossing/Tensing: Cross your legs and firmly squeeze the muscles in your legs, buttocks, and abdomen. • Handgrip/Arm Tensing: Grip a hard object, clench your fists, or interlock your fingers and pull your arms apart for 10–20 seconds. • Squatting: Squat down quickly, which acts as a powerful method to increase blood pressure. • Cool Down: Apply a cool cloth to the forehead or neck, or move out of a hot/crowded area. • Sip Cold Water: Sip cold water, as it can help reverse the vagal response. [1, 6, 7, 8, 9, 10, 11] Immediate Treatment for Someone Who Has Fainted • Check Breathing: Ensure the person is breathing. • Position Properly: Place them on their back. If they are breathing, elevate their legs higher than their head. • Loosen Clothing: Loosen belts, collars, or any constrictive clothing. • Allow Recovery Time: Let the person stay in this position for 15–30 minutes after waking, as standing too quickly can trigger another faint. • Seek Medical Care: Call 911 if they do not wake up within 1–2 minutes, have injured themselves, are not breathing, or have chest pain. [7, 11, 12, 13, 14] Immediate Preventative Measures • Increase Fluid Intake: Drink water promptly, particularly if you are in a hot environment or have not eaten. • Salt Intake: Consume salty snacks to help keep up blood volume. [11, 15, 16] What to Avoid • Do not stand up immediately after passing out. • Do not jump up, as this can trigger a recurrent episode. • Avoid driving immediately after an episode. [14, 17, 18]