Keflex and difficulty breathing

I was on keflex 500 mg every 8 hours. After four doses, I experienced dizziness, difficulty breathing and syncope. I also had palpitations, high blood pressure, ice cold hands & feet and continued to have dizzy spells while lying flat on my back. None of the labs done in the ER could explain this. It's the keflex. I have taken penicillin before without any adverse reaction. I will never take Keflex again.

Ive been on keflex for a day and a half and have difficulty breathing... I am done with this med ...im calling my doctor first thing in the morning

I took one and have severe vomiting for four hours and had difficulty breathing. I did not take any more.