Bedsheets (I assume you mean something denser like quilts or bed covers), heavy drapes, etc, would help deaden the room, but it would work mainly on higher frequencies, I think it would make the sound muddy and muffled sounding, though a little of this treatment would be better than nothing (the whole dead end, live end thing).
If you look at the acoustical testing done on the various panel materials, you'll see it takes much thicker and denser material to have an effect on lower frequencies.
I am far from an expert, this is just from memory when I researched the panels I ended up with.