She could have hurt herself due to being sedated, falling off a bed and hitting her head, or getting up to go to the bathroom and hitting her head in there.
Possibly, but if she was so heavily sedated as to be fatal, would she have enough strength to move at all? I suppose it is possible that she managed to struggle to the bathroom perhaps to vomit, and fell and hurt herself. I find it doubtful that simply rolling out of bed on to a carpet or whatever would necessarily result in a bloody injury.
Again, explaining the presence of blood is the part the doesn’t seem to fit the scenario of accidental overdosing.