You aren't scratching the back a lot, are you? If you are getting excessive wear and tear in the back and you are using a satin pillowcase (and not scratching a lot....I used to make that mistake), chances are it's one of two things:

1: The hair in this particular unit started out a little on the "fried" side

or

2: You need to change up your maintenance products, mainly your shampoo

Also, do you wash in cool water? That can prematurely dry the unit and cause shedding.

If this is a regular occurrence I can almost guarantee that your shampoo has something to do with it. People don't realize this but shampoos are the "silent killer". They may lather well, smell nice, and feel like they are doing their job as you are washing, but if you aren't using a gentle shampoo that is made to protect fragile processed hair, over time the result is that it will damage the hair little by little to the point where you have a problem but have no idea what has caused it.

Also....silicone based products can greatly reduce friction.