The Patient Who Made Me Doubt Myself

I've been a nurse for five years now, but one patient from last month still haunts my thoughts. Mr. Thompson, an elderly man suffering from dementia and paranoia, often accused nurses of stealing his belongings or undermedicating him. One night, in frustration after dealing with similar accusations all day, I snapped and told him off harshly. It felt awful as soon as the words left my mouth. He looked so hurt and confused. Is it normal to lose patience like that when caring for difficult patients?