Struggling Recovery with AML

My father was diagnosed with AML in October of 2010. He is currently in remission, however he is struggling with a large set back. He was doing really well, starting to get around and out of the hospital. He then contracted Thrush and has had a set back. He has a temperature, suffering from confusion (names, places, even words to say), and not able to eat due to sore throat and nausea. We are now back in the hospital, and after an MRI scan and blood work nothing has come up as to why all this is happening. They will not even say that the fever is from the thrush, just that it is an unrelated fever. The doctor is going to bring in a radiologist to take a look at him, (spinal tap) while he was home he took a few tumbles trying to be too independent walking to the bathroom. They are also looking into having a radiologist come and look at him. I was wondering if anyone else out there has had a similar reaction after total body radiation and bone marrow transplant, and could give me some insight on to what might be the cause. I am afraid that my father is struggling with this backward movement, being mentally and physically warn out after everything he has already gone through.