something that causes a state of strain or tension.

"#stressors can place a tremendous burden on relationships"

 Stressors are situations that are experienced as a perceived threat to one's well-being or position in life, especially if the challenge of dealing with it exceeds a person's perceived available resources

Examples of internal stressors include:

Fears. Common ones include fear of failure, fear of public speaking and fear of flying.

Uncertainty and lack of control. Few people enjoy not knowing or not being able to control what might happen. ...

Beliefs. These might be attitudes, opinions or expectations.