While standing, a shooting pain ran through my left leg & knee. my leg pulsated majorly for 5 seconds. i massaged my knee after. what could that be?

Lumbar radiculopathy: Shooting pain in the distribution you've described sounds like a radicular pain from a lumbar L4 nerve root which in your scenario is most commonly from a bulging disk, although there are many other causes of this. If this issue persists consider talking to a neurologist to see if you need additional studies like MRI L-spine and EMG/NCS of your left leg to exclude motor lumbar radiculopathy.