The Doctor knew he wasn't feeling well when he sent Donna home, he hadn't really wanted to, he just didn't want her to see him suffer, The goodbye had been hard for him, he had hugged his good friend with tears in his eyes before walking back to the TARDIS. Though the Doctor knew he would miss her, he sighed and leaned on the console of the TARDIS and takes off. His body was trembling and he was so unwell. The Doctor was gone for weeks, he wasn't really able to fly the TARDIS so he ended up back on earth crashing, He was just too ill to fly his precious ship. Groaning the Doctor shakily tried to get to his feet.
"Oh I'm so sorry." He whispered. He went to check his ship, but he collapsed passing out. He forgot Donna still had a key.