Use ～てならない in written or formal spoken Japanese to say that a feeling or impression keeps welling up and you can't suppress it — typically 思えてならない, 気がしてならない, 残念でならない. It suits reports, emails and speeches where you want to convey strong personal conviction or regret without sounding emotional or colloquial. Compared with ～てたまらない (physical urges, casual) it is more literary and limited to inner feelings and spontaneous perceptions.