I had a similar thing happen.
I found that taking prescription levels of zyrtec can prevent it (2 pills/day).
I think what is happening with me is the T is aromatizing to E. This E spike makes mast cells more likely to degranulate, spiking histamine. This, combined with my minor allergies, sets off labyrinthitis, causing benign dizziness. Blocking histamine prevents the labyrinthitis. One way to tell if this is whats happening with you, is to just try taking an antihistamine before your injection. If it prevents the dizziness, then your dizziness is histamine mediated, and not likely a serious problem.
But really, you want to prevent the E spike in the first place, because it doesn't only cause histamine spikes, but also makes you more likely to be emotionally labile, put on fat, and have higher levels of many inflammatory factors. The way to prevent the E spike is to inject smaller doses more frequently, so you don't trigger your body's aromatization threshold.
If taking antihistamines doesn't prevent the dizziness then you may have a more serious problem on your hands.