The condition you are referring to is called "cognitive impairment" or "cognitive dysfunction." It is a broad term used to describe a range of conditions where a person experiences difficulties with cognitive abilities, such as memory, attention, problem-solving, and decision-making.
Cognitive impairment can occur due to various reasons, including neurological disorders, brain injuries, certain medical conditions, medications, substance abuse, and mental health issues. In some cases, a person may exhibit intelligence and proficiency in certain areas but struggle with others, leading to occasional or specific instances of seeming "stupid" or senseless.
It's important to note that using terms like "stupid" can be stigmatizing and hurtful. People with cognitive impairments deserve understanding, support, and empathy rather than derogatory labels. If someone is experiencing cognitive difficulties, it is essential for them to seek proper evaluation and medical advice to determine the underlying cause and receive appropriate care and support.