Synonyms for Agonizing:

adj.

difficult and painful, suffering (adjective)
excruciating, tortuous, racking, disturbing, tormenting, harrowing.
disappointing (adjective)
heartbreaking.
painful (adjective)
distressful, cutting, unbearable, throbbing, arduous, woeful, uncomfortable, annoying, crushing, grueling, irritating, hurtful, aching, disagreeable, oppressive, chafing, miserable, bothersome, anguishing, harrowing, offensive, inflaming, painful, severe, cruel, horrendous, Torturing., Irksome, piercing, troublesome, withering, tormenting, Cramping, wrenching, biting, aggravating, grievous, trying, smarting, acute, insufferable, Gnawing, bitter, excruciating, burdensome, unpleasant, odious, Besetting, stinging, sore, stabbing.
punishing (adjective)
confining, anguishing, chastening, Incarcerating, burdensome, Persecuting, punishing, distressing, penalizing, Disciplining, Crucifying, tortuous, Imprisoning.

n.

bad, chapped, chronic, burning, crippling, angry, achy. tragic, terrible, pain, sad, unhappy, depressing, heartbreaking, upsetting, dismal. undecided, torn, irresolute, reserve, be a toss-up, agonized, indecisive, be thinking of/about doing something, indecision. agonizing (noun)
harrowing, torturesome, torturous, painful, Torturing., excruciating, agonising.
excruciating (noun)
disturbing.

v.

lamenting (verb)
Decrying, Sighing, whining, grieving, crying, snuffling, Bewailing, sniffling, moaning, Bemoaning, Whimpering, wailing, lamenting, longing, clamoring, groaning, sobbing, Ululating, weeping, mourning.
paining (verb)
racking, Paining, Afflicting, Discomforting, distressing, hurting, stitching, suffering.
punishing (verb)
Persecuting, chastening, confining, Keelhauling, reprising, executing, Incarcerating, Correcting, Crucifying, Burdening, Fining, avenging, punishing, Pillorying, judging, Imprisoning, lambasting, penalizing, Disciplining, Castigating, Sentencing, Chastising.

Other synonyms:

chapped, torn, indecisive, irresolute, achy, angry, crippling, indecision. undecided, agonized, burning. bad. reserve. Other relevant words:
achy, pain, agonized, bad, sad, torturous, heartbreaking, tragic, depressing, angry, agonising, torn, reserve, upsetting, torturesome, burning, disturbing.

Usage examples for agonizing

  1. The suspense became agonizing – Cord and Creese by James de Mille