Are sundowning symptoms unique to dementia? could normal people feel agitated, irritable, or restless during sundown hours? i feel uneasy at sundown hours ever since i was a child. so i was "born with" dementia?

No, you do not have dementia and those symptoms are not even consistent with dementia.

Sundowning is but a phenomenon that occurs in Alzheimer's patients, but on its own is not at all pathagnomonic, or definitive. You can be born with cognitive injury, but dementia is acquired as we grow older, both from genetics, or degenerative causes, in the main.