How does this work?

Felt pretty good all week and then last night, out of the blue I sneezed. Then sneezed again. I took a hit of vitamine c, went to bed and woke up about 4 am with a sore throat and my sinus filled with some serious cloggage. Now I am sitting at work having problems focusing on anything and feeling aches attempting to take over.

It was like someone flipped the sick switch on me.