Hi thanks for your question
You felt electric shock
while blood sample was being taken from your vein for test.
This can happen as nerves at many places accompany the veins.
So there are chances that during taking out blood sample the nurse stimulated nerve by needle and you felt, like electric shock.
Now feeling same sensation again can be explained by the fact that needle might have slightly injured the nerve or nurse has deposited a small amount of drug by side of nerve which has irritated the nerve and when you touch the vein nerve is again stimulated and gives you same sensation.
Hope I answered your question.