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Attempt to wake the person with a loud noise. Administer painful stimuli. Ensure that you have called 911. Check if the person is breathing. Check for a pulse.
Try yelling, "Are you okay?" and shake the person gently. This may be all it takes to bring the person back to consciousness. If the person is unresponsive to your questions, but you are not sure whether she is "unconscious" to the degree that requires CPR, then you should administer a painful stimulus to see if it produces a conscious reaction.  The most common form of this is a "sternal rub," which entails making a fist and using your knuckles to rub vigorously into the person's sternum or breastbone. If the person responds to "pain" — to this sensation — you can continue to monitor her without CPR as this is a sign that she is okay for the moment (if she does not respond to pain, however, you will likely need to proceed to CPR). If you fear the person otherwise has a chest injury from the trauma, other methods of testing her pain response include pinching the person’s fingernail or nail bed or pinching the person’s trapezius muscle (back of the neck). The pinch should be very hard and directly to the muscle.  If the person responds to the pain by either curling all her limbs in or out, this is referred to as posturing and could be indicative of spinal injury. You likely have already done this, but especially if the person is unresponsive to pain, you need to make sure that an ambulance is on the way.  Remain on the line with the operator, or if someone else is there, hand the phone to him so he can receive further instruction. If the person is unconscious but breathing, then you may not have to perform CPR, especially if no one around is certified in the practice.   Be sure to keep a constant watch on the rise and fall of the person’s chest to ensure that he’s still breathing. If you cannot tell by watching alone, you can place your ear near his mouth or nose and listen for breath sounds. When you listen at someone's mouth, point your head down his body to the chest and watch his chest rise and fall at the same time. This is the easiest way to see breathing. Note that if you have any reason to suspect a spinal injury but the person is breathing, then do not try to reposition him unless he vomits. In this case, roll his entire body to the side while supporting his neck and back to keep them in the same position.  If you have no reason to suspect a spinal injury, then roll the person onto his side, position his top leg so that both his hip and knee are at a 90° angle (to stabilize him on his side), and then softly tilt his head back to help keep his airway open. This is called the "recovery position" and is the safest for the patient to be in, in case he vomits at any point. You can check the person's pulse on the underside of her wrist on the thumb side — called the "radial pulse," or by gently feeling one side of her neck about an inch below her ear — called the "carotid pulse." Always check the carotid pulse on the same side of the body on which you are sitting. Reaching across the neck of a patient for her pulse can cause panic if she wakes up.  If a pulse is absent at any point, and especially if there is no breathing, now is the time to start CPR if you are trained; if not, follow instructions of emergency medical personnel over the telephone.   If you accidentally hung up after initially calling them, you can call back at this point for further instructions. They are trained to provide instructions for laypeople over the phone.