i) There is no question of asking another passenger for your own reserved seat.
ii) Sleeper berths are for each passenger (6 passengers) under 3-tier sleeper coach and all 6 have sitting rights in the day time on the lower berths....
iii) The railways intention is to provide berth / sleeping accomodation between 9.00 pm and 6.00 am hours only.
iv)...
more... What is sleeper ticket ? ... it is sleeper reservation either berth or RAC.
v) If it's not sleeper confirmed or RAC, then it's WL ticket and those WL ticket holders are entitled to travel in unreserved general coach.
vi) You can buy unreserved ticket - General Coach.