D&Dtools1

A creature targeted by this spell loses the ability to dream during sleep or rest.
Rather, in place of dreams, the target's slumbering mind is filled with the sounds of a discordant orchestra.
After the victim's first attempt to sleep, he incurs a -2 penalty on all Wisdom-based skill checks.
This penalty persists as long as the symphonic nightmare effect maintains its hold on him.
This spell affects all creatures that sleep or enter sleeplike trances; creatures without the need to sleep are effectively immune.
In addition, the creature's sleep is now haunted.
It can no longer gain complete rest from sleeping or resting.
The target does not regain hit points or heal ability damage naturally, nor is it able to prepare spells if doing so requires a full night's rest.
The creature is, however, now immune to the dream and nightmare spells, as well as to other effects that cause nightmares (such as the night hag's dream haunting ability).
The caster can lift the effect of this curse at will, but it is otherwise difficult to remove a symphonic nightmare before its duration expires.
A remove curse cast at a higher caster level than the symphonic nightmare spell removes it, as does a successful break enchantment.
Otherwise, a wish or miracle is required to lift the curse.
Focus: A small statue of an opened skull within which is arranged a miniature orchestra.
The quality of this component must be extraordinary, giving it a value of at least 1,000 gp.