How to overcome sleep?

Hello Hive account@steemians..
I need your help..i am facing a severe issue..
And i am much worried about it.. Issue is this whenever i started to visit steemit and start reading articles to comment ,appreciate and try to engage with community i felt sleepy.. After some time it became difficult to awake myself.. I felt much tired and sleepy..
Why it is so? Does anyone else also face same issue..? Or its only my problem.. May be its due to reading on cell fone.. I am not habitual.. This issue was with me during facebook searching
I have some health issues like asthma allerjy and using steroids on daily basis..
Dont knw the reason but i cant continue reading for long period..
Can anyone tell me about it...