There is a story that says that the Bulgarian climber who died a week ago on K2 may not have been properly acclimatized. Apparently he had only arrived at K2 a week before.
In the normal turn of events a climber will goto C1 and head back to base camp as the first part of the acclimatization. Then next time they might head to C2 before heading back to the base camp. The Bulgarian climber though on his first climb up the mountain went to C1 and rather than head back down, decided that he would try get to C2. George Dijmarescu reported that he looked dazed at even C1.
Also another factor is that his porter was supposed to have stayed with him throughout to check that he was alright. But it turns out the porter headed back down to base camp without telling anyone. So no one knew if the Bulgarian was in trouble or not.
During the night there was heavy breathing coming from his tent. This can be normal on K2 where people find it harder with so much less oxygen.
The Bulgarian climber had books that dealt with the effects of altitude sickness on him. So he would have known that the effects that he was feeling were related to one of those conditions. He probably died from high altitude cerebral edema or HACE. The latter is where the brain swells. it can be caused by going up too high too fast.
At least one good thing is that he appeared to have died peacefully. He died in his sleeping bag.