Hi, welcome to the forum, dementia can be associated with the sleep disorders. They usually have a shallow sleep - mostly stage 1 and 2 - and are easily awakened. They also have trouble turning in bed, and i also associated with restlessness in bed. Sometimes patients may be awakened by choking episodes at night that are triggered by sleeping on their backs.
These can be effectively treated by addition of dopamine agonist dose against prescription at bedtime. Patients of dementia with Lewy bodies disease have a high incidence of rapid eye movement (REM) sleep behaviors. Nocturnal confusion can also be seen. This is also treated low doses of clonazepam against prescription. I suggest you to consult neuro physician. Take care and regards.
Does your father have any symptoms of sleep apnea? It can cause frequent awakenings, and if the oxygen level gets low, maybe it could affect his thinking when he wakes.
Some meds are known to have sleep disruption as a side effect.
Finding the root cause of his segmented sleep is important, as sleep deprivation can cause meory loss and disjointed thinking, and you don't want him to get misdiagnosed.