once I realized that most days I spent entirely at home made me feel awful when they should make me feel rested, I started making a point of getting out of the house on days where I have nothing planned. you can really go anywhere as long as it's a place that you're comfortable and can waste some time in. I would usually go to a coffee shop and do homework/browse the web on my laptop, which I could just as easily do at home but it felt better than doing it there because I actually had to get up, get ready, get outside, and interact with people even if minimally. it just helped me stay grounded.
nowadays if i have to stay home I make a point to force myself to get up at a normal time (sleeping until past noon will make you feel like you can't do anything because it's already so late you migh as well just stay in) and do something creative, usually that helps the time fly if you get engrossed in it for a while. having a hobby is a great timesink that actually feels productive.
if the weather is nice, just go outside and take it in. if you can walk around your part of town, just putting on music an meandering can be a good way to get familiar with your area or find something new to try. I'm a fan of biking so if there's a pedestrian trail in your city just get on and ride. I've found that putting on music and going at a chill pace I can end up wasting hours taking in the sights and vibing and actually get some excercise too.
in general, moving around and getting out are huge. you don't even need to be doing anything ""productive"". but if you must stay inside, get out of the bedroom and find an activity you can get lost in for a while, stimulate your mind a bit.