I've felt that way too. You just lack motivation. Watch something inspiring and motivating. If it's about studies I could recommend Dragon Zakura (it's a Japanese drama about dumb kids who get into Japan's most prestigious institution. You can watch it with English subtitles). Sorry I only know Japanese and Korean dramas and shows. Cartoons and animes about hyper inspired main characters (like Naruto) can also be good.

But if you don't like to watch Japanese stuff, I am sure you can find many inspiring shows and movies. Children's movies are especially particularly inspiring. Even if they are childish. When you feel like a child again, your worries will disappear and you will be able to get the same enthusiasm and energy that all children have.

But these things will only work for a short time. It good to set goals and reward yourself for goals. It increases your motivation to work harder.

There will always be periods of time in life when you will feel like this. It is just normal among people. Don't let yourself think that you can't get out of it. It will pass. One day, even without your realizing, you will suddenly start feeling chirpy again.