Shift workers frequently sleep badly regardless of how carefully they arrange their day. The reason is that the difficulty is one of timing rather than of sleep habits, and timing is set by a system that does not adjust on demand.
Sleep is being attempted against the clock's signal
The internal clock generates an alerting signal that peaks in the evening and is at its lowest in the early hours, and it is set by the external day.
A night worker attempts to sleep in the morning, when that signal is rising, and to work when it is at its lowest.
The result is shortened daytime sleep and impaired alertness overnight, which occurs even when the person is thoroughly tired.
The clock adjusts slowly and only with consistent cues
Shifting circadian timing takes several days of consistent light exposure and behaviour, and the shift is gradual rather than immediate.
Most rotating rosters change faster than that, so the adjustment never completes before the schedule changes again.
Permanent night workers do better in principle, though many revert on days off to be with family, which resets the clock towards the day schedule each week.
Daytime sleep is shorter for reasons beyond the clock
Daylight, household noise, deliveries, phone calls and social obligations all interfere with sleep taken in the morning.
Sleep obtained at the wrong circadian phase is also lighter and more fragmented in itself, so the two effects compound.
The typical consequence is a shortfall accumulating across a run of shifts, which is why fatigue tends to be worst on the final nights of a block.
The effects are recognised occupationally
Error rates and reaction times deteriorate through a night shift and are worst in the early hours, which is reflected in how safety-critical industries schedule work.
Long-term shift work has been examined in relation to several health outcomes, and it is treated as an occupational exposure rather than a lifestyle choice.
This is why rostering rules, break requirements and limits on consecutive nights exist, though the specifics differ substantially between countries and industries.
What tends to help within the constraints
Consistency is the main lever available: keeping sleep timing as stable as circumstances allow, including on days off, reduces how far the clock is moved each week.
Controlling light around sleep, and the direction of rotation when a roster moves, both influence how badly the misalignment develops.
Persistent sleepiness that continues on rest days, or falling asleep unintentionally, is a matter for occupational health or a doctor rather than for scheduling adjustments alone.