Why does face look different when I tie my hair up, in comparison to when I wear it down?

Casper: It is because with your hair up, it is putting upward pressure on your eyebrows and facial skin.  A ponytail acts a bit like a nonsurgical facelift and browlift.  I think one of your concerns is that you have somehow damaged or permanently changed your face by wearing your hair in a ponytail for 12 years, and that is simply not the case.  A browlift and facelift would make the same changes permanently and you would look even better than when your hair is up!  Best of luck. 

By tying hair up in a tight ponytail, you are actually
lifting the tissue above and below your ear, creating a lift. When hair is tied
up, you are likely to see a tightened brow, wider eyes and defined cheek bones.
However, when you wear your hair down, the lift is lost and facial laxity can
cause these features to appear less defined, and in some cases sag. Without
pictures it’s impossible for me to suggest a treatment or procedure, but be
assured that surgical intervention may not be required.

You  have discovered that a ponytail hair style gives you more of a lifted/youthful facial appearance.  When you were younger there wasn't much of a difference with hairstyle change.  As the face gets older, one gets more of a noticeable lift effect with wearing the hair pulled up.  Rest assured, wearing the hair in a ponytail for many years did not cause any accelerated aging of your face.

Wear your hair up may indeed generate traction on the face that could change the distribution of skin and fat. In a way it may give you an idea of a component of a facelift.

Your pony tail is actually lifting on the tissues above and below your ear creating a lift. When you wear your hair down, the lift is lost and you're beginning to see the effects of aging. There was an interesting product marketed recently called the facelift bungee which basically took advantage of this temporary lift effect. The only permanent option to remedy the sagging skin is a lift procedure to tighten and reposition the sagging tissues. I hope this information is helpful for you.Stephen Weber MD, FACSDenver Facial Plastic Surgeon

The only answer I can come up with is that when you tie your hair in a pony tail, the tension placed on your facial  skin and scalp is in a backwards and upwards direction. On the other hand when you  let your hair down the weight of your hair and natural gravity allows the facial tissues  to droop more.

You are giving yourself a daily "ponytail" facelift!  By pulling your hair into a pony tail you are lifting the facial tissue and creating a smoother appearance.  When you release the ponytail the tension is released revealing your natural face.  You have not coaused any damage by wearing your hair up each day.  If you are unhappy with the appearance of your face when its natural then there may be a range of facial rejuvenation options to address your concerns. A comprehensive review with a fully qualified plastic surgeon is your best next step.

You are inadvertently creating a 'ponytail' facelift when you hair is up. When it is down the tension on your facial skin is released, revealing your natural skin sag and shape. This does happen in long-term use of tight ponytail hairstyles.

Sometimes pulling on the hair can pull the face a bit and make it look slightly differently. Hard to say without seeing you in person.

I can'r address your concerns specifically, but I also suggest people to look at closely at before and after photos for changes to the hairline ans these are fairly common changes that can make people look odd or unnatural. Share your concerns with your plastic surgeon to see if he or she might have suggestions.