1To writhe or roll about (usually from pain); to be in physical agony.
事故で負った傷で彼は床の上でもだえていた。
He was writhing on the floor from the wounds sustained in the accident.
虫歯の激しい痛みにもだえて眠れなかった。
I couldn't sleep because I was writhing in severe toothache.
やけどをして苦しげにもだえる。
He/She writhes in pain from the burn.
2To be anguished or tormented; to be mentally troubled or in emotional agony.
将来の進路について悶えている学生が多い。
Many students are anguished over their future career paths.
失恋の痛みでもだえて、数週間は外出もしなかった。
He/She was so anguished by the heartbreak that they didn't go out for weeks.
決断を先延ばしにして悶えているだけでは何も変わらない。
Nothing will change if you just agonize and keep postponing the decision.