I was born with hyperopia and astigmatism, while the astigmatism stayed about the same, i went from +4 sph to -2 sph (6 dpt!!) from age 19 to now 28. how worrisome is this? will progression ever stop?

Substantial change: Yes, progression should slow down. You're correct that this is a large swing in prescription. I would wonder if there is any systemic condition or medication that you've been diagnosed or given. Diabetes can result in vision change and so can medications like topamax, (topiramate), sulfonamides, & Prednisone to name a few. Your ophthalmologist would be keen on addressing these possibilities, otherwise monitor.

Changes with age: welcome to adulthood- usually, eye changes as described begin in the mid 30s- however, unfortunately, progess with age, Do yourself a favor and get an ophthalmolgy evaluation to rule out any medical eye issues.