Alarmingly long freeze followed by a hard boot. A couple times a day. Been there, done that.
Your description was accurate but for me it wasn't Budgie, it was Firefox.
Since I could never open HTOP (being frozen and all) I started opening it before the freeze and killing FF when it got wiggy. It was FF, usurping all available resources as it did and taking the unit into deep freeze. It got patched but I switched browsers anyway and it never happened again. This was all not long ago, and quite how I remember it going down...my hardware is old, too. My point is maybe more that one factor at work here...