Welcome to HCM,
After going through history of your father he has Diabetes
and Hypertension of > 15 years duration, I presume both are reasonably well controlled, and now regarding your question is it possible to have raised creatinine
levels and improve in i week time yes due to many reversible conditions like dehydration
may lead to Azotemia and infection which if treated may be reversible , even many drugs which are nephrotoxic can lead to rise in creatinine and if drug is removed and treated may improve quickly.
In his case if BP was low at the time of hospitalization renal blood flow is compromised and may cause creatinine level to go up and improve with treatment.
If he is suspected to have chronic kidney disease
which is possible in his case due to Long standing Hypertension
Please have faith in treating Physician,We doctors always do what is best for patients.