"painful realization" is correct and usable in written English.
You can use it to describe a feeling of dismay or regret that comes with understanding a difficult truth about oneself or one's circumstances. For example: "She had a painful realization that she had been wrong all along."
For many South Africans, facing up to that painful realization is becoming their main focus.
After a rather painful realization, she accepted Ms. Overman's suggestion that she create and stick to a budget.
Many decades ago, after I'd come to the painful realization that I was never going to be a good musician, I gave away my saxophones.
My tears were evoked by the painful realization that the author and the reviewer are both simply too young to know what they're talking about.
At the same time, despite the excitement of seeing militants marching in the cities, leftist activist networks are buzzing with the painful realization that contemporary protest is broken.
"Divergent" clearly has thrills, but it also movingly explores a more common adolescent anxiety — the painful realization that coming into one's own sometimes means leaving family behind, both ideologically and physically.
That and some nasty dreams he has been having about his mortality drive him into memories of his youth and painful realizations that come better late than never.
Expect defecation and heartbreak, masturbation and painful realizations.
They never demonized those of another socioeconomic class, and always told the full story - that of self-doubt and painful realizations.
What a painful, horrible realization that must have been!
But gratitude also comes with a painful partner the realization that not everyone is afforded the opportunities that I am, that not everyone is forgiven the way that I've been forgiven.
