Meditation on floor vs bed
It depends on why you are meditating. However, since you are posting to a Buddhist group, look at it from the Buddhist perspective.

Meditation supports the Buddhist way of viewing the world, with non-attachment, that sees the impermanence and lack of essence of all things, especially one's "self".  As such, "Creative Attacks" are not relevant to this practice.

Further, if you are going through rough patches (or creative attacks), then the application of meditation is to look into this rough patch (or creative attacks), to see the characteristics mentioned above, but especially the illusory nature of the "you" who is suffering these rough patches (or creative attacks). 

That is, instead of trying to combat feeling with feeling, work on seeing the illusory nature of the source. When confronted with suffering, look for the one who suffers, and when that is seen to be an illusion, the suffering becomes a non-issue.

Having said that, the posture to adopt to meditation should be one in which you can be alert (nothing that will lull you to sleep) while minimizing your discomfort.  Certain postures may make some bodily sensations more noticeable than others, so I'd recommend the one that reduces those.  Beyond that, you're free to pick a posture.