One time i was given a shot of morphine for a headache in the er and my head started spinning around, got dizzy and nauseous. does that means i'm allergic to it?

Morphine: you are not allergic but may be intolerant. there is a diffrence between the two. allergic reaction with come up with itching, red rash, sob or wheezing and swelling pf face lips and throat. It is a reaction because of release of histamine in your system.

No: More likely side effects. Narcotics are rarely used to treat headaches currently. Another choice may work better. All the best.