Same here. To the point where it is a good predictor of a cold/flu coming on.It also ignored the phenomenon of feeling better just before a crash. This happens for some people coming down with a cold or flu. They suddenly feel symptoms lifting, then get sick a few days after. When it happened to me I experimented restricting further my normal (in)activity to see what would happen. The crash wasn't caused by activity and I am guessing it is some strange immune system effect.