The snake in a dream has mostly a symbolic dreaming...
According to some, the snake symbolizes negative feelings you might have... If you have a stressful and threatening situation, then you need to acknowledge that you have those feelings and deal with them.
In your waking life do you have any situation that seems difficult? Do you have any negative feelings piling up?
Let's say that the snake is your negative feelings... your being afraid to be bitten, is being afraid to acknowledge that you have them, and deal with them...
by falling of the bed and having a bump on your head, is the aftermath of not wanting to deal with what is going on in your subconscious...
My guess is, this dream is a warning that you have some negative feelings inside of you that you have to deal with them, before you "fall of the bed"... if you do recognize them, accept that you have them and deal with them, then
you will reach some clarity about yourself...
you may also undergo some transformation that was bound to happen sooner or later, and it can be either the easy way (interpret the dream on time, and deal with your feelings, reaching clarity with no pain) or the hard way (fall metaphorically off the bed, having the bump on your head, but at the very end reaching clarity with a little pain that could have been avoided).
I hope I gave you a head start to do some soul searching of your own...