A character breaks a solemn vow. The consequences stem from the powers that observed the oath's swearing.
Pronouncement
Whatever vow the character made, it came with an implied warning that guilt and restlessness would beset anyone who broke the oath.
Burden
The character is plagued by restless sleep and recurring nightmares featuring those the character swore to protect. The character gains 3 levels of exhaustion that can't be removed until the curse ends.
Resolution
The curse lasts until the character upholds the broken oath. That might require the character to wait until the circumstances arise again or, more questionably, to engineer the circumstances.