I sometimes feel guilt when I do not do something creative or productive. Is it ok to just lay in bed some days?

The important thing is to really feel satisfied. If you feel relaxed, ready to go forward, happy; that's good. But if you feel guilty you need to react, change your unproductive and uncreative behavior, and try to find motivation. If the reason of your laziness is lack of motivation, lettin go and staying in bed is not a solution. You need to build solid routines. I personally would suggest you to wake up real early in the morning (4:30 AM) for a few weeks, finding some time to accomplish tasks in the early morning: your days will never be unproductive anymore