What about nightmares?.
Allah's Messenger (PBUH) said in narration of Abu Hurayrah: "Dreams are of three types: one is a good dream, which is a sort of glad tidings from Allah, the evil dream which causes pain is from Satan, and the third one is a suggestion of one's own mind, so if anyone of you sees a dream which he does not like, he should stand up and offer prayer and he should not relate it to the people" (Sahih Muslim 2263), and as narrated by Abu Qatada: "I heard the Prophet (PBUH) saying a good dream is from Allah, and a bad dream is from Satan, so if anyone of you sees something he dislikes, when he gets up, he should blow thrice (on his left side), and seek refuge in Allah from its evil for then it will not harm him" (Sahih Albukhari 5747), and in another narration of Abu Qatada also: "One should not disclose it to anyone, and if one sees a good vision, he should feel pleased, but should not disclose it to anyone but whom one loves" (Sahih Muslim 2261 f).
Thereupon, the true vision is one that a believer sees and it is a blessing from Allah so that the believer may rejoice or take heed, and the bad vision is suggested by Satan to frighten the believer as he whispers to him of sorrows and fears, and the third type of dream is the reflection of one's thoughts and experience one has during wakefulness. So if Satan shows man frightening things he cannot comprehend, he should remain silent and ignore it and not tell anyone about it for it will not harm him, and it is recommended to stand up and offer prayer so that the fear in his soul may go away or to seek refuge in Allah from it and spit three times to his left, and turn over from the side on which he was sleeping, as Jabir bin Abdullah narrated that Allah's Messenger (PBUH) said: "If anyone sees a dream which he does not like, he should spit on his left three times, and seek refuge in Allah from the Satan, and let him turn over from the side on which he was sleeping" (Sahih Muslim 2262).
And as narrated by Jabir bin Abdullah: "A Bedouin came to Allah's Messenger and said Messenger of Allah! I saw in the dream as if my head had been cut off and I had been moving on haltingly after it, thereupon, Allah's Messenger said to that Bedouin Do not narrate to the people the vain sporting of Satan with you in your sleep, and Jabir said I heard Allah's Messenger (PBUH) saying in his subsequent address None amongst you should narrate the vain sporting of devil with him in the dream" (Sahih Muslim 2268).
Satan can impersonate any form or person to frighten the believer and make him worried and sad, except for the form of Allah's Messenger (PBUH), as Allah's Messenger (PBUH) said in narration of Abu Sa'id Al-Khudri: "Whoever sees Me, then he indeed has seen the truth as Satan cannot appear in My shape" (Sahih Albukhari 6997).