i just watched tracy edwards testifying against jeffrey dahmer. there's something i'm confused about

for anyone who doesn't know, tracy edwards was hand cuffed and held at knife point by dahmer for several hours in 1991. i believe he was the only victim that ever successfully escaped from dahmer. i watched tracy testifying( https://www.youtube.com/watch?v=qGLHDqcV-Pg&t=18s ) and it is so heartbreaking. i was in tears several times because you can really how (obviously) hard this all is on tracy.

he details everything that happened that night. he had met dahmer earlier in the night, he liked dahmer and said he was very nice and friendly. tracy trusted dahmer enough to go back to his apartment with him.

he then goes into detail about how out of seemingly nowhere, dahmer had hand cuffed tracy to himself. when tracy looked over he saw dahmer had also pulled a knife on him. tracy then talks about how from that point on, dahmer was going in and out of intense moods every 30 minutes or so. dahmer would go between about 3 moods.

sometimes he would be normal and friendly, as if they were just hanging out normally.

then sometimes he would get very extremely aggressive/angry and would threaten to hurt tracy and make him do weird things. tracy said that during the angry moods it was as if dahmer wasn't the same person, his entire personality and even the way he looked would completely flip.

the 3rd mood was basically just silence, as if he wasn't even there anymore, almost like a trance. he also talks about how certain times thru out the night dahmer would start "chanting" and rocking back and forth (all this happened while he was still hand cuffed).

that was the part that confused me. not that i don't believe tracy because i believe everything he said 100%, i just want to understand what was going on with dahmer. why were his moods cycling so quickly and drastically? was he dissociating at some points? what was the chanting and rocking about??

i mean i know we're not in his head so we can't know for sure but i guess i'm asking about the possible psychology behind it? this kind of thing is very interesting to me and i'm hoping someone here knows more about this stuff than i do. i just want to understand as best as i can