Welcome to HCM
We understand your concerns
I went through your problem descriptions. Human being feel tirred nd sleepy after heavy work physically or mantally or sometimes due to internal physical illnessess such as anaemia
and some other wasting disease. But these internal problems do come with other symptoms your GP should identify correctly.Tiredness
after physical or mental strain usually go away after one or two deep and resting sleep and with some nutritious food. There is another aspect which is worth mentioning here. Mental tiredness tend to stay more because as a human being our body likes to rest more and our mind allows it to do so.
Everyone wants to take rest and be idle but their duties and responsibilities don't allow them to do so. Therefore mind is the actual key of body. Urgency and duty keep mind going and inturn mind makes body to move do its duty. Keep your mind engaged in the duties and make the duties priority than sitting idle.
You may consult a GP and get your pathological and vitals check done.
Hope I am able to answer your query. Available for further clarifications.