I recently went to a full install of Ubuntu 16.04 LTS. (I was dual booting for a while) and now there are no other operating systems on my laptop. So I have it on my hp -2000 laptop that is a few years old but still has a 400g hard drive and 12g of ram. I do notice though if I have had the laptop on for a while (say from 8am till about 12pm) It starts to act sluggish. Keystrokes are delayed is really the biggest issue. If I power cycle it comes back good as new and there is no issue. Is this a problem other folks have had? Is it just my bad laptop?
In a case like this, I'd plug in an external USB-based keyboard and see if the sluggishness is on that one, too. If the problem follows that external keyboard then it could be that your computer is sluggish because it's busy.
I'd then try to figure out what it is that's making my computer busy.
How do you find out which program is using too much memory? So maybe you could consider running something like gnome-system-monitor, for example, which might give you some insight into what's running. If this is related to a processor-hog stealing all its time then this could help.
If it's a bad driver then I'm not sure I'm the right guy to help.