Concentrating on learning has the same effects as concentrating on work: If you don't take care of yourself and overdo it, even the most interesting topic will lose its fun aspect.
So, if you find yourself learning for a longer period of time, make sure you manage your energy levels well. No matter whether sitting in front of the computer taking an online course or sitting in a training room, it is important to take small 2-5-minute breaks if possible every 20 minutes.
Here are actions that you can do either separately or in combination with each either. My extra tip: Set an alarm clock so you don't forget!
Open your window and take slow and very deep brea