Am i confused of depressed? can't think as fast or sharply as i used to.

Depressed or anxious: The most common reasons for a sudden decrease in ability to think as quickly or sharply as you used to in someone your age are depression or anxiety. Depression has such a significant impact on brain functioning that it has been said to cause "pseudodementia" a condition that looks like dementia but isn't. You should see a psychiatrist or primary care md.