What Causes Nausea, Blood Pressure, Fainting, Blurry Vision And Sickness?

I am a farm wife (48 ) that has iron absorbtion problems due to gastric bypass surgery 8 years ago. I have been feeling nausaus for about 2 hours tonight, my blood pressure is usually 116/75 . I have taken it three times tonight and it is 92/52.. I feel faint, blurry vision, almost sick. I gave myself a b-12 injection about 8 hours ago like I do every month. Should I be scared? I do not feel well