Sir, if we sleep by sitting on chairs (especially during night shifts) , is this gives as much rest to body as we sleep on bed? or any health effects?

No: Poor sleep quality, back and neck strain. Considering you are getting paid for doing it, you have to make a decision if it's worth.

Not usually: Natural sleep involves resting of your brain and relaxation of all your muscles. Your body turns from side to side to avoid constant pressure on your back, so you won't get stiff when you wake up. Sleeping in recliner may help but not in chairs. You may get much more restful to sleep in bed.

Not as restful: While sleeping upright in a chair, some of your muscles are still working to keep you upright, which could signal to your brain not to have a very deep, restorative sleep and cause daytime fatigue, decreased concentration, body aches among others. Sleeping horizontally allows your body to relax and enter into the 4 sleep stages that are crucial reset and repair your body.