Why do horned lizards sleep so much?

Horned Lizards are reptiles. This means that they are cold-blooded animals. Being cold-blooded, they have to warm themselves up to be able to move around during the day. This can sometimes make them appear as if they are very sleepy, as they sit in one spot basking in the sun for an extended period of time, waiting for their blood to warm enough for them to go about their day.