"Bed rotting" - which translates as "rotting in bed" - is a very popular trend recently on TikTok. Referring to the hashtag, people post videos of themselves wrapped in a blanket, with a phone in hand or something to eat.
The phrase describes staying in bed all day. In short, it's like a lazy day, but with less activity, because during a lazy day, you can engage in activities that you find fun, while perhaps spending time with friends and family.
Staying in bed for more than a day or two is worrying and can indicate various mental health problems. This type of behavior has been linked to symptoms of depression and anxiety, among other mental health conditions.
Sleep hygiene may be at risk. If you want to relax somewhere, choose a comfortable sofa or chair.
Being tired after a long day is normal, but if it interferes with your work, social life or other important activities, then it's a good idea to discuss your symptoms with a doctor.