~면서 : progress conjuntional ending &gt; while ~ing
~서 : emphasis conjuntional ending. > in condition that~
If you say "누우면서 공부할 수 있어요." ,it means that you study for a short time
while you are lying down. So this sentence doesn't make sense.
"누워서 공부할 수 있어요." =I can study in condition to lie down.