Not Medical Advice: If you mean hand falling asleep as temporary numbness in hands, the fastest way is to sit on it until you feel the sensation of "pins and needles".
Sources suggest that the nerve becomes hypersensitive after being pressed on,” and becomes irritated. This general feeling of tightness and tingling ensues while your veins bulge. As per Womenshealthmag.com, this happens because blood isn’t returning to the heart—at least, not until the temporary blockage of blood flow is released.
While this “falling asleep” sensation can occur in any body part where soft tissue can compress on nerves and blood vessels, areas protected by bone (inside the head and chest, for example) won’t be affected.
While the numbness or tingly feeling that ensues can sometimes be alarming (especially when it takes a while to go away), most of the time, it’s really nothing to worry about.
Please note that if you ever experience numbness or tingling and it doesn’t resolve after a few minutes, or if it happens randomly, call your doctor.
Learn more about the causes of tingling in hands and feet at WebMD.