sick in bed
Bedridden due to illness. He worked himself so hard in the lead-up to Christmas that he ended up spending the whole holiday sick in bed. Our mom has been sick in bed for the last week, so we've all had to try to pick up the slack around the house.
sick in bed
remaining in bed while (one is) ill. Tom is sick in bed with the flu. He's been sick in bed for nearly a week.