No, not nightmares: HP Lovecraft began experiencing the parasomnia ‘night terrors’ from the age of six. Night terrors cause the sufferer to physically move or scream to escape waking dreams, and are estimated to affect 3% of adults. HP dreamed of what he called “nightgaunts” which later appeared in his books as thin, black, and faceless humanoids that tickle their victims into submission. Lovecraft’s affliction fed into his dreamlike, nightmarish prose, but also fuelled it. 
H.P. Lovecraft is a famous writer best known for writhing The Call Of Cthulhu.
In a 1918 letter, he wrote:
Do you realise that to many men it makes a vast and profound difference whether or not the things about them are as they appear?... If TRUTH amounts to nothing, then we must regard the phantasma of our slumbers just as seriously as the events of our daily lives...