What Causes Elevated Body Temperatures While Lying Down?

I've been checking my temp for the last 3 days and around night time I'm running between a 98.3-100.3. I use a forehead thermometer and the right side always comes out hotter than the left. I don't feel sick. Sitting up I'm around a 99.3 which is normal for me but letting down I go up to a 100.3. Once I sit or stand up I'm in the low 90's or 98.3. What causes my temp to go that high while I'm laying down? Should I be concerned?