Question: what are the causes of low energy?
Answer: Diet. A poor diet or nutritional deficiencies may cause people to have low energy levels. ... 
Exercise patterns. People may notice that their energy levels decrease after they spend a long time without exercising. ... 
Low testosterone. ... 
Sleep apnea. ... 
Insomnia. ... 
Depression. ... 
Anemia. ... 
Thyroid disorders.