We stay in the deep for about 45 minutes and then if we are deeply disrupted we come back up into light sleep. It is normal to have five 45 minutes deep sleep cycles in an 8 hour period. Anything that upsets these cycles will cause sleep problems. If you work the night shift and sleep during the day, there are many things that can disturb your deep sleep and awaken you during your light sleep phase. Noise is the biggest problem.
Daytime sleepers have to contend with noisy neighbors, children, traffic, lawn mowers and such.
When looking for a home to rent or buy, always look for one in a quiet neighborhood. Look at the house after school hours and on Saturday when the neighborhood kids are home from school and day workers are home mowing their lawns. Look at the house more than once at different times of the day. Make sure the house is not near any train tracks, noisy factories, or airport fly-bys. Make sure the bedroom is in a location as to not be near the street or noisy neighbors.