Kesha's Mom Sues Dr. Luke -- He Gave Me PTSD

Kesha's mom has countersued Dr. Luke ... claiming he tormented and abused her by allegedly date raping her daughter.

Pebe Sebert claims in her legal docs -- obtained by TMZ -- Luke did indeed rape Kesha in a way "as not to be tolerated in a civilized society." She claims she now suffers emotional distress and post-traumatic stress disorder as a result.

Pebe is largely restating the claims Kesha has made -- that Dr. Luke gave her a date rape drug and raped her. But she also adds new detail, claiming Luke would brag about taking girls out on a first date, get them drunk and then "f*** them in the ass."

Pebe also claims Luke dealt drugs to entertainers -- which she says is how he acquired the name "Dr." -- during his 10-year run as a guitarist on "SNL."

Luke has denied the claims made by Kesha and Pebe, saying it's all a ploy for Kesha to get out of her contract with him.