Even though he said he was fine, Donna knew something wasn't right. With every step, he seemed somewhat weak and fragile. But every time she tried or wanted to say something, he would get there first. When he turned and asked her if she was coming, she frowned slightly and shrugged her shoulders. She headed towards the door after the Doctor. 

"There's something not right with you." She muttered under her breath so he couldn't hear as she stepped out of the time-machine. Before she could say anything, her breath hitched in her throat. 

The planet they were on was beautiful. Two suns hung in the air, one closer than the other. The setting was filled with colors of all different types, with a forest of trees not far away. Donna could see no sign of civilization.

"So what do you think?" The Doctor asked her. She glided forward another few steps, taking in a lung full of the fresh alien air. 

"It's lovely, Doctor, what are we-" As she was talking to him, she turned to find him clutching his stomach, a pained expression on his face. Dark circles seemed to have formed under his eyes, and Donna felt her heart flutter with panic.