Usually nothing. Occasionally the thing you must not play through.
You take a hit, your head snaps sideways, and a hot electric line runs from your neck down one arm. It goes dead or weak for a few seconds, then clears, and you go back in. Almost every defensive back and lineman has had one.
Most of the time that is exactly what it is — nerves at the base of the neck got stretched, and they recover in seconds to minutes. But three things change the answer, and coaches and parents should know them cold.
Both arms. A stinger is a one-arm injury. Symptoms in both arms is a spinal cord sign, and that athlete comes off the field and gets evaluated the same day.
Neck pain. A stinger does not hurt the neck. If the neck hurts, something else is going on.
Weakness that stays. Seconds to minutes is a stinger. Weakness still there days later is a nerve injury that needs looking at.
Nobody goes back with weakness or neck pain. And if you are getting them repeatedly, that is a pattern worth fixing — usually neck and shoulder-girdle strength, sometimes equipment fit — rather than something to keep absorbing.