Strange Negative Emission

Today, I did a blessing on one of my friends who is in the hospital, by their request. Something strange happened that never did before when I did any kind of blessing. For about 2 minutes after I was done, there was a strong feeling of negativity that hit me. It was so influential that I had to sit down, and I left shortly after it began to subside. I am not sure what this was, and I was hoping someone here could give me some insight. What I did was a basic blessing. I cleansed them with purified water, then prayed to Zeus, Apollon and Athene for freedom, healing and strength. I'm sure there are several possibilities, but I really don't know where to begin theorizing.