Even to this day I will occassionally suffer from anxiety after an injection. It is very unerving and can quite literally make a grown man panic like newly deflowered mormon.
Take note that the introduction of any drug can cause idiosyncratic reactions, which is a term the medical community attaches to undocumented reactions to an administered drug. Anxiety, shortness of breath, tremors, and fast heartbeats can all occur. It's mostly psyhcosomatic so try to stay calm and focus your attention one something else. Most of us have been there and know what it feels like.
PEACE