I read that you are not held accountable for what you dream. But what about lucid dreaming? Are you accountable for sins committed then?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

A dream is what a person experiences during sleep; Ibn ʻAtiyyah wrote, “A man is said to be dreaming if fantasies occur to him in his sleep...” [Al-Muharrar Al-Wajeez fi Tafseer Al-Kitaab Al-ʻAzeez: 3/248]

Al-Qamoos Al-Muheet (p. 1096) reads, “The words 'hulm' or 'hulum' is what one sees in his sleep...”

If this is established, then if the person is actually asleep, he will not be held accountable for anything that he experiences during his sleep because the hadeeth asserted that the sleeping person is not liable for any religious assignment or obligation during his sleep. The Prophet, sallallaahu ʻalayhi wa sallam, said, “The Pen has been lifted (i.e. actions are not recorded) from three: from the sleeping person until he awakens...” [At-Tirmithi]

As-Sanʻaani wrote, “The phrase 'The Pen has been lifted' is a metaphor indicating that those in the mentioned states are relieved of the religious assignments and obligations because all the actions of those competent for religious assignments are recorded (by the Angels). Allaah, The Exalted, says (what means): {And indeed, (appointed) over you are keepers, noble and recording.} [Quran 82:11-12] The Prophet, sallallaahu ʻalayhi wa sallam, used the expression 'The Pen has been lifted' to indicate that the person in such a case is relieved from religious assignments: one of which is while sleeping. As long as the person is asleep, he is not liable for any religious obligations or assignments and will not be held accountable for anything that he does or sees (during his sleep)...”

However, if the person is not actually asleep, then he will be held accountable for his actions, as long as he is conscious.

As for the lucid dreams, if the person does certain practices so as to enable him to summon erotic thoughts and sexual fantasies to mind during his sleep, then it is impermissible for him to do so. Scholars stated that it is prohibited for the Muslim to call erotic thoughts and sexual fantasies to mind because this may lead to committing Zina (fornication/adultery).

The Permanent Committee for Islamic Research and Fataawa was asked, "Is it permissible for the unmarried Muslim man to fantasize about having sexual intercourse with his future wife?" The answer reads, “It is prohibited for him to do so because it may lead to committing fornication and evil deeds...”

The Permanent Committee for Islamic Research and Fataawa was also asked about a man who frequently fantasizes about having sexual intercourse and ejaculates and whether it is considered masturbation; or the case when he deliberately thinks about sexual intercourse so as to ejaculate and achieve sexual arousal and pleasure. The answer reads:

"If such erotic thoughts and sexual fantasies accidentally cross the person's mind, then there is no harm in that, as evidenced by the hadeeth narrated by Abu Hurayrah in which the Prophet, sallallaahu ʻalayhi wa sallam, said, ‘Verily, Allaah has pardoned my community their mistakes, their forgetfulness, and that which they have been forced to do under duress.' [Al-Bukhari] Another version of the hadeeth reads, 'Allaah has accepted my invocation to forgive the whispers in the hearts of my followers, unless they put it to action or utter it.' However, when the person intentionally visualizes having sexual intercourse, ejaculates, and attains sexual arousal and pleasure, then it is incumbent on him to perform ghusl (ritual bath) because the ruling of janaabah (state of major impurity) is applicable in this case. If he intentionally calls erotic thoughts to mind and has sexual fantasies every now and then, then such an act is impermissible and unbecoming of the Muslim; it contradicts the Muslim's noble manners and sense of honor. The Muslim should abstain from engaging in such actions and preoccupy himself with lawful and useful activities that benefit him in the worldly life and the Hereafter in order to distract himself from indulging in satisfying sexual desires through unlawful means. It should be noted that such intentional stimulation of desire to achieve sexual arousal and pleasure through unlawful means is detrimental to the health and the intellect; it is feared that one might incur grave consequences.”

Allaah knows best.