The current guidelines for tourniquet use suggest a one-hour maximum for restricted blood flow to upper extremities and a two-hour maximum for lower extremities, but also admit that the onset and degree of tissue death (necrosis) varies according to patient age and physical condition. Past these thresholds, restricted blood flow can result in nerve damage. (The tingling you feel is your nerves’ way of expressing angst—a call to roll over before they get really pissed.)
After four hours without blood flow, wet gangrene and the decomposition of tissue due to stagnant blood trapped in extremities can begin. Generally, your arm will not fall off due to gangrene (as might a finger or a toe); rather, if you allow the infection to progress (the timing of which varies widely), you will be forced to have the arm amputated rather than allowing the infection to become systemic. If not, you will die. Though, this is unlikely to happen to even the soundest sleepers.
The short answer: It’s not good to restrict blood flow for more than about an hour and a half; it’s very, very bad to restrict flow for more than four hours.
I expect comments thanking me for the following illustrative image.
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