What are these dips near my undereye and how do I get rid of them? Is it collagen or fat loss? (Photos)

It can be confusing to try to figure out which procedure works best for the aging eyes and who to ask. A midface lift is also a great option for many people to correct malar bags & usually leads to a more dramatic reduction of lower eyelid fat bags compared to just a blepharoplasty. The recovery & downtime is very minimal. There are usually no drains, most people can go out the same day, you can shower the next day and most patients take no pain medicine. There are never any guarantees of course with any procedure whether it is surgical or nonsurgical in nature. 
Surgery is not for everyone though. In today's day and age, there are many nonsurgical options to consider although surgery usually gets the most improvement specifically of the cheeks, neck and jowls. Aging liplines, volume loss in cheeks, forehead wrinkles and skin tone can be nicely improved with injectables and laser treatments.
I would recommend that you see a board-certified plastic surgeon in your area that is a member of both ASPS & ASAPS and performs a lot of mini facelifts and neck lifts but also offers all the nonsurgical options such as injectables and laser treatments. Go over your concerns with them and make sure above all, you walk out of there with several options and an idea of the pros and cons to each of them as well as realistic expectations.
I hope this helps and wish you all the best in your surgery and event. If it does, please take a moment to up vote this answer on the “respond” button on the top right. 

From the photos it appears you have a tear trough deformity. This is can be fixed surgically by addressing the lower lid fat and cheek. Fillers could also be a good option. I recommend seeing an eyelid expert in your area.
Best of luck.