Welcome to the forum.
Open Task Manager > More details (at bottom) > Click Memory tab. Keep an eye on any culprit/s there.
Do you use sleep more often than shutdown, or do you have hibernation enabled? Do you have a lot of browser tabs open and/or different browsers at the same time?
Or is it more weird, like randomly when just idling on desktop?
Make sure you have an active Paging File too. Or when you run out of physical RAM, that's it - total system freeze not just slow down.