Everyone here pretty much hit the basics. I'd have to go simpler and say straight chemistry. If you have it you know, if you don't you never will with that particular person. Don't try to force something that isn't there.
@voyaj I am very experienced with Ketamine sex although after what I went through(addiction, bodily damage, borderline psychosis) with that drug I cannot advocate its use to anyone. The sex is interesting, to say the least, but honestly I'd rather have sex really stoned, on LSD, mushrooms, or quickly after coming down from breaking through on DMT.
You will have alot of trouble getting an erection or even getting interested in the girl during K foreplay. Mixing it with MDMA has helped this. Or VIGOROUS handjobs. Your girl will have to jerk it like her life depends on it. And my girlfriend tells me it was way more comfortable to be in a K-hole during sex than sitting next to someone. [you forget who they are and stuff when in the hole] so she will be obliged to try. Once you get it in you will be good to go for A LONG TIME. Sometimes it feels like your whole consciousness is in your genitals. Sometimes it feels like your consciousness is floating around the room watching your two bodies have sex.
Often, you are not quite sure which of these bodies (if either of them) is yours. At deeper levels I lost all memory of being human and tried to understand what I was witnessing. I would come up with ideas of 4 legged creatures (the beast with two backs) And sometimes it even felt like I was watching two aliens have sex....if that makes any sense. I was so far removed from reality that even the very human activity of copulating was not understandable in terms of this world. My girlfriends face would shift between aliens, animalistic images, goddess like images, and ugly versions of herself. She said the same happened with my face.
When I went out of my body into a full K-hole I would either come back sitting next to my GF with a limp dick. Or, I was robotically annihilating her with masculine force.
Other than the orgasm, which is strange and different from any other drug I've had sex on (not really "better" IMHO) your body feels kind of numb as others have noted.
Stay away from K if you have any sort of addictive personality. It will MESS UP YOUR ORGANS!....not cool. [and if you get ketamine bladder it hurts to have sex] REALLY NOT COOL
Favorite sex drug is a tie between LSD or VERY strong Kava with cannabis.
In the province of the mind what one believes to be true, either is true or becomes true within certain limits. These limits are to be found experimentally and experientially. When so found these limits turn out to be further beliefs to be transcended. In the province of the mind there are no limits. However, in the province of the body there are definite limits not to be transcended.-J.C. Lilly
The Spice must flow
Zat was Zen and dis is Dao.