system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come when you have a fever and your temperature is so high you feel cold?
gpt
Because the way a fever works is by tricking your brain into thinking that your normal temperature is *supposed* to be higher.  So, instead of 98.6 degrees, your brain might now register 104 degrees as its desired normal temperature.  So suddenly your core body temperature is 5 degrees lower than it "should" be, so you feel the same as if you didn't have a fever, and your core temperature had dropped to 93 degrees.

Further, even once you get your core body temperature up to the brain's desired fever range, the air around you is a lot colder compared to your temperature than normal.  For instance, if you're running a fever of 104, and you're in a room that's 72 degrees, it feels the same as not having a fever and being in a room that's 67 degrees.