See a doctor and get blood tests done such Hb, CBC,
Vitamin B 12 levels,
Thyroid function etc. There may be many different reasons so it has to be investigated. Plus having a regular sleep wake cycle , regular physical exercise and good diet are prerequisites. The existence of the biological clock can be particularly apparent when it's off kilter: Jet lag and shift work can throw our normal patterns out of tune and take a toll on physical and mental health. Even shifting the clock an hour forward or backward can disrupt our biological clocks.