I do not have dementia, but I get confused in evenings in hospital. Why?

Many reasons. When one is in the hospital one is usually ill, you aren't in familiar surroundings and medicines and meals are often not on your schedule. Delirium can also lead to confusion and is common in older adults and in hospitalized people.
Depends. The answer depends on whether you are a hospital employee or inpatient, young or old, have chronic illnesses with multiple medications or otherwise in good health.
COMMON IN HOSP. Very common in hospitalized patients; days and nights get confused.