Flipping your schedule on days off. 

Snapping back to a "normal" schedule every weekend creates a constantly shifting clock that worsens both sleep and sleepiness.

Cost: you never adapt in either direction

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Light at the wrong time. 

Morning sun on the drive home tells your brain it is daytime and pushes your sleep later, so you lie down wired.

Cost: shorter, lighter daytime sleep.

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Caffeine too late in the shift.

Caffeine has a half-life of about 5 hours on average, taken before bed it measurably cuts total sleep time.

Cost: you fall asleep, but lose an hour or more of the sleep you needed.

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Unplanned dozing 

In one large study, 7% of workers fell asleep unintentionally on the job at least once a month, and shift work raised that risk.

Cost: safety and a clock that gets even more confused.