1.

First of all friend....not all ppl can study for 3-4 hrs a stretch...take me for eg..i cannot sit more than 1. 45 hrs altogether.

I know  it feels difficult when u come to know about others studying vigorously and we study for a very short duration......frnd we have to accept the fact that god has not given all so much endurance....only a select few manage it...

One way out (as suggested in many earlier topics) is that u study for 1 hr( since thats ur limit) .then close  ur book and take a brk for 15 mins........

this way keep on studying  and taking breaks so that in this way u feel freshed everytime u start studying and are able to enhance ur efficiency....

2.

regarding the fact that u are joining bansal....keep pne thing in mind that by seeing others studying so much arnd u ...u will also develop the zeal in u to start studying......and believe me..once u are motivated i am sure that ur body will not allow to start feeling dizzy after 1 hr..

so all the best and never ever think that u are in a bad state of affairs when u are reading 6 hrs and others are reading 12 hrs( keep in mind that 6 hrs of efficient reading is much more imp that 12 hrs of sloogish reading..)

Cheers!