If your partner shows signs of being late to work frequently and is in a bad mood, this behavior is MOST consistent with:

The behavior described is most consistent with burnout, which is a state of physical, emotional, and mental exhaustion caused by prolonged and excessive stress. In the context of the emergency medical services environment, burnout can manifest as signs such as frequent tardiness and a negative mood. These symptoms reflect the cumulative toll of chronic workplace stress, lack of support, and feeling overwhelmed by the demands of the job.

Burnout can lead to an overall decrease in job performance, negatively impact relationships with colleagues, and result in disengagement from work responsibilities. Recognizing these signs in a partner is crucial, as it indicates that they may need support to address their well-being and mental health.

While acute stress could present with similar issues, it typically involves more immediate reactions to a specific incident and may not be characterized by a consistent pattern of behavior over time. Drug use could lead to changes in mood and reliability, but the symptoms described in the question do not directly point to substance-related issues. Delirium is characterized by confusion and a change in mental status, which isn't reflected in the partner's described behavior. Hence, burnout is the most fitting interpretation of these signs.