I am using my K1000 while lying in bed sometimes. A small pillow under the head is required and I use to position them so that the headband rests on the upper forehead or a bit above, while the earpads are pushed more to the temples - the front earpad rests on the lower part of the temple, to be more precise. Thus, the headphones are still pretty much in an upright position - not completely vertical, but vertical enough so that they don't fall.
To be honest, I prefer the sound this way too since I get both more details and fuller bass as opposed to the "normal position" presentation due to the drivers being closer to the ear - this in trade for a bit of soundstage, but that is more than enough anyway. The same effect can be obtained to a certain degree by using the phones in a more closed in position, but that results in a tradeoff that is absent when lying in bed as described above: the mid-highs become more "splashy" and dominate the upper highs, I suppose because of the reflections between the driver / baffle and the head. I think that in the "in bed" position the cranium surface corresponding to the headphones is in an angle against the driver / baffle (as opposed to being - almost - parallel when in "normal". completely closed in position), so that there are less multiple reflections. Think two mirrors that are either (almost) parallel (listener upright, phones closed in) or at an angle (listener lying down, phones a bit open and in the position described above).
I usually keep my K1000 open enough so that when I'm in normal, upright position I can put a finger between them and the earlobes, I guess that's ~25 degrees open or so.
I second mmmayer167 though, you should be very careful as to avoid falling asleep with the K1000 on your head, it happened to me several times and it's quite dangerous for these babies. For sleeping with the headphones
I much prefer the Stax 303, although I have managed to crack one of their plastic forks this way. K501 are tougher, lighter etc. - perfect for sleep except for their lesser sound (as compared to the other two).