it can still be an issue with memory even if it isn't as blatant as "out of memory".

The easy example being a datastructure growing over time and getting slower to manipulate and query. This is a problem where being cavalier with the amount of memory you allocate and use will hurt you, even if you've got lots of memory to spare.

We'd need to know how much memory Atom itself is using after that time. Perhaps GP has found a memory leak, perhaps he's on an Atom processor; we don't know unless he tells us about resource use by Atom itself.

You might be right. At any rate it felt like an Atom issue, as I've not experienced lag like that on Bluefin, Geany, and other similar editors.