Trying to balance on his knees with his abdominal and back muscles cramping was a trick, one born of necessity and prefected over years. Still it's obvious he's struggling.

Due to the dryness in his mouth and throat speaking was complicated. And mentally sooner part of him was still that boy trying to make sure all useful things got parted out.

Finally, with effort, Vader manages, "Need a bacta tank." It's weak, him paying rapidly between words.