(India, Maharashtra, Nasik)
Dehydration is of course the major cause of feeling sleepy and tired all the time. There are other causes too, like depression, anxiety, B12 deficiency, improper diet (low nutritional intake).
For me life changed in just a second due to an accident I met with an year back. Before the accident I was full of energy, perfect emotional n physical balance. I was totally healthy. I used to do pranayama and meditation.
But that accident landed me into a series of health problems including physical n emotional.
B12 deficiency was the typical problem which was hard to detect and proved very very bad for my physical n emotional health. Even after I started taking B12 shots, I was nervous bcz of the accident. and that caused many more problems. I always used to feel sleepy, tired.
then I started concentrating on my food and pranayama. I drank lots of water throughout the day. I ate vegetables and fruits. especially dates and apples. this gave me good nutritional input. Then i started the magical pranayama again. Pranayama itself, if done properly, cleans ur mind, improves all ur biological cycles, metabolism anabolism etc, functioning of each n every cell of ur body. It literally lifted me from those health problems and made me a perfectly healthy man!! very balanced mind! when u r balanced from inside, from ur breathing, then those around u feel it. In just 3 weeks again I became perfectly healthy.
if u want to know how to do pranayama, see this video.
Its in Hindi. They have told 7 pranayamas in series, but I do only four of them daily (bhastrika, kapalBhati, bahya, anulomVilom) which takes only 22 minutes and gives 24 hour energy, freshness, health, better relations, better focus, concentration literally everything!!!