Computer freezes if not in immediate use

My computer runs perfectly fine if I'm at the helm and typing, or doing anything basically. But if I leave my computer, watch tv for 5-10 minutes and come back it's frozen...

well, not exactly frozen, but it takes minutes for even the windows bar to load. Every action becomes very very slow. It resets upon restarting the computer, and I can go about doing everything normally unless I walk away from the computer for a short while then it slows.

If I put my computer to sleep, it comes back fine as well; which seems to be the only way to walk away from the computer unfortunately. I've searched many ways to fix "freezing" and haven't had much luck finding similar slowing down problems anywhere on the internet. Reinstalled windows 10 as well and it doesn't seem to help.

I have a pretty old computer I put the parts together myself, but it's worked fine for 5-6 years at this point. I'm not sure what would be failing first though, but I am in the market for upgrades soon. I use a SSD if that impacts the situation any.

Maybe it's entering suspension state?. Check Energy settings.