Probably the chick is just resting. Make sure there is room in the brooder for them to get away from the heat source. What you should have, is one end that is heated, and one end that is not. The chicks will choose where to be most comfortable at any given moment, and as long as they can get away from the heat, they will do that rather than overheat. I don't measure the temperature in my brooder with a thermometer - I measure it by the chicks' behavior. When they are huddled together in a corner, they are cold. When they are spread out, panting and lethargic, they are too hot. When they are moving around comfortably, pecking at the feeder, getting a drink, taking a nap under the heat and then moving away from it for a little while, the temperature is just right.