There can be many reasons as to why you are feeling sleepy during the day. It can be that you just need more sleep if you are not getting enough at night or keep waking during the night. There are also medical reasons as to why you may be feeling tired. Lack of vitamin B12 is often a cause of tiredness and brain fog. It often goes undiagnosed for years. Low iron or Ferritin levels can also cause you to feel lethargic. Blood cells carry oxygen around the body to the organs that need it to enable them to produce the energy they need to function. A lack of red blood cells means your whole body has to work a lot harder to get the energy it needs in turn making you feel tired. A full blood count will be able to show if you are lacking iron. You may need supplements for at least 6 months if your iron levels are really low.
An under active thyroid is another cause of feeling sluggish and tired. The thyroid produces thyroxine and this is what controls out metabolism. If this isn’t working as it should you may need to take medication to raise your levels back to normal.