Beardies will often lay flat against warmer surfaces in an attempt to raise their body temperature. 85 degrees is definitely too low for daytime temperatures and it's likely that he's doing it to warm himself up. You'll have to find a way to keep his basking spot between 100-110 degrees throughout the day, but that really shouldn't be too hard even with the AC on. My beardie's viv is right next to my AC and even with it blasting out cool air it only drops his basking temp a few degrees.
Shedding may contribute to that behavior, too; sometimes they'll drag their body across the floor or their rocks and other furniture and then just lay flat. However, I'm sure it has more to do with the cooler temps.
