Honestly, Ukitake hadn't wanted to stay abed, but he'd been recovering from another bout of illness when he had arrived, and the shock of being transported in an instant to another world had set his lungs off again. There wasn't much that could be done for it aside from rest. He'd explained, quite thoroughly (and, he hoped, patiently) to the nurse that his illness was both incurable and not at all contagious.
At least it had only been a brief attack. Ukitake was able to sit up and smile when he felt Ichigo approaching, and to call out the young Soul Reaper's name without taxing his lungs overmuch.