Not all synthetics are the same, but polyester fill definitely isn't what I'd call a good quality filler. It doesn't breathe at all, traps heat. I get it because I had the same pillow until I switched to a down alternative cooling pillow. The filler has thermoregulating properties, air flows through, and the pillow always stays cool. The sweating stopped the very first night.

Have you seen a doctor? My friend had something similar where she was sweating terribly in her sleep. Turned out she had something like pre-diabetes or something like that. Better not let stuff like that slide.

The room's not hot, AC is set to 72 degrees, blanket is thin. The pillow is just a regular synthetic fill one, maybe that's the problem?