Hi; I study mathematics/theoretical physics. I learn a lot of stuff (advanced math/physics theory); but after few month; feeling like I forget everything I learn. Why? for example; I am working 7/24 mathematics (in academic year); after I am resting in the summer. I do not read anything in the summer months. and then I feel like I forget everything when I start again study. Why? My motivation in this case does not remain. I feel very bad. also when I dont work (study) for a long time; then I feel reluctant when I want to study. in short; is this normal ? Thanks.