[SIZE=+1]You can mention you had a nightmare but no need to go into details. Also, there's no point mentioning it to others as they will only ask what was it about.
Otherwise, If you have a nightmare.
Spit to your left (three times).[SUP]1
[/SUP][/SIZE][SIZE=+1]Seek refuge in Allah from the Devil and from the evil of what you have seen (three times).[SUP]2[/SUP][/SIZE][SIZE=+1]
Do not speak about it to anyone.[SUP]3[/SUP][/SIZE][SIZE=+1]
Turn over on your other side.[SUP]4
[/SUP][/SIZE]
Reference:
[SUP]1[/SUP] Muslim 4/1 772.
[SUP]2[/SUP] Muslim 4/1 772, 3.
[SUP]3[/SUP] Muslim 4/1772.
[SUP]4[/SUP] Muslim 4/1773.
There came to him (the Holy Prophet) a desert Arab and said: I saw in a dream that I had been beheaded and I had been following it (the severed head). Allah's Apostle (may peace be upon him) reprimanded him saying: Do not inform about the vain sporting of devil with you during the night.
It was reported that Abu Qutaadah said: “The Prophet (peace and blessings of Allaah be upon him) said: ‘Good dreams come from Allaah and bad dreams come from the Shaytaan. If any one of you sees a bad dream which makes him afraid, let him spit drily to his left and seek refuge with Allaah from its evil, then it will not harm him.” (Narrated by al-Bukhaari, 3118; Muslim, 2261).