Good to hear you came through it. That sounds frightening. I think starting low and going slow is safest. 50 mg of nad+ seems high; from what I have read these are short-chain amino acids that work best with gentle, gradual signals. Lower amounts should reduce the risk.
I was doing my usual shots before leaving for work. After placing 50mg of NAD+ in the hip, blood came out when the needle was removed. I figured I must have hit a vessel there for the first time but paid it no mind. Roughly 15 seconds later a sudden wave hit: vision turned bright white, head pressure felt ready to burst, arms and chest went from tingling to burning, breathing grew difficult from the tightness, and dizziness nearly dropped me. I assumed a heart attack or allergic shock. With the phone in another room I grabbed the epi-pen from the drawer hoping it would give time to reach help. I had the cap off and was ready to use it when the head pressure eased and breathing got easier. I waited another 15 seconds or so until it passed.