short term illness from training?

Most times after training kickboxing or BJJ at the gym, I get home and feel like I've got some low-level fever. Skin flushed and hypersensitive, sore throat, feel really hot (although temp is normal) etc. The harder I work, the more prominent the symptoms are. A good, long nap or a good night's sleep will eliminate the symptoms.

I'm guessing I'm allergic to something at the gym. FWIW, I otherwise only really workout at home and I feel fine, but then again I don't exert myself nearly so much so I don't have much of a comparison to give....

Any ideas?