Naps do not detract from the subsequent night's sleep. Half of the world naps and calls it a siesta. Many suspect that REM sleep relaxes the mind and non-REM sleep the body. Sleep is one of them. Travel with time zone changes upsets the rhythm temporarily.
Mental problems causing sleep disturbance are three times more common in younger adults.
The commonest psychiatric problem in the elderly is very treatable depression. Sleep apnea is repeated 10 second periods of stopping breathing. Continuous nocturnal positive pressure through the nose can treat this. Others need minor surgical nasal passage correction. Restless legs is a strong urge before sleep to repeatedly move ones legs preventing sleep.