Worried about my schnauzer she's showing strange behavior?

Max is 15 1/2 yrs old and has been dx with spindle cell cancer. This is her second round of this cancer which was removed 2 yrs ago and it grew back in the same place. She has been well for close to a year since her recent dx in Oct 2009. In the past month she has been having problems where the vet has put her on famotidine,prednisone and tramadol. Last week she had a bad bacterial infection in her stomach, she wouldn't eat,drink and was vomiting, since then she has been put on antibiotics and anti diarrheal meds. She is now doing well in that respect but has been exhibiting strange behavior. I think she has dementia, it seems to affect her mainly at night. She wanders the house, or she'll just stare into space like she sees something I don't see. She has gotten more clingly to me too. Her breathing sounds bad but the vet took xrays three weeks ago and it showed clear lungs. Has anyone else ever had problems with their dogs with this strange change in behavior? Any comments would be appreciated and might help me. thanks