suddenly changing behaviour

For roughly 5 years maybe there's been the same cat living around my house. Our landlord and I have helped take care of and look after her (gender assumed based on fur pattern) all this time. Even though she doesn't allow us physical contact since she always runs 5 feet away and just stare...

My cat has been acting strangely since this morning. He keeps walking around in slow motion, sniffing everything. He has been getting freaked out by things left lying around the house that have always been there. He is acting like he is seeing hallucinations. He is an 1 year old indoor Scottish...