if you want to get in touch with this energy system and exploit it safely, you may read "Daoist Nei Gong" by Damo Mitchell.

some other e-books talks about advanced internal energy working practices, that leads to extremely deep meditation, dead man like, breath/blood flow/cerebral activity stoping. But this may be way too much for you for now, just know that it's normal and nothing to be scared about. Western doctors are way too blind to know such Eastern epic hidden knowledge.

you can find the pdf e-book on internet for free if you search well

if you seek further info, you can find on internet much info about what happens during your sleep and how your conciousness moves from the lower body (physical) to the middle (etheric) and to the highest (conciousness body) and how it goes back when you wake up.

well it's a freaking huge topic but very interesting.

have fun discovering your hidden potential.