21 momth old Son wakes up warm everyday

My son has been consistently waking up for the last 4 days with a 100 degree temp. I know this isn’t a fever or not even a low grade fever, some people told me, but it’s strange to me that he’s this warm only after waking up.

Like he’s warm enough that he gets groggy and doesn’t wanna get up. I have to go in and get him up or he’ll just keep lying around.

He goes to bed in a t-shirt and diaper only and our air is set at 70 degrees. His room is not hot by any means it’s actually sort of cold so I’m so confused about it and it’s worrying me because he’s prone to have febrile seizures.