Highest I've ever been...let's see.
It would have to be the combo I did with my girlfriend at the time for my 16th birthday.
This is how it went:
Consumed 3.5g of dried mushrooms. Once the peak came, we waited about an hour (cuz you know, we wanted to experience an unadulterated shroom trip before we dipped into the rest of my stash). So once we were tripping balls, I consumed 2 pills that were a very strong dose of MDMA/MDA (the gf took one). Waited for that to kick in. Once that hit, shit was fucking bliss. Like the visuals were just fucking magical and the love and empathy were through the roof. Once the peak hit, we went and smoked a nice fat joint of some primo weed. That made us feel even better.
Then I busted out the Ketamine. Started taking little bumps. Holy mother of fuck was that INTENSE. Like, maybe its just me, but has anyone ever noticed that once you start doing K on other hallucinogens (especially shrooms) the hallucinations and visuals begin to take on a more mathematical and geometric shape? Like absolutely BEAUTIFUL polygons. The measurements, the scale, the flow and rippling of the visuals...it was mind boggling.
Then, what really sent me into another world, was when I started filling up the balloons with nitrous. My gf at the time didn't wanna bump the K, cuz she wasn't as "crazy" as I was back then, but I convinced her to take some nitrous (cuz we all know how it feels when you take in a full balloon of nitrous while on GOOD MDMA) - to call it bliss would be a massive understatement. We each inhaled at the same time and held that shit in. Then at the exact same time we both fell back onto my couch and managed to hold onto each other. I recall forcing my eyes open just to look at her, to see her beauty (and of course to make sure she was okay). Her eyes were so far back in her head you could only see white. I kept focus on her for a little while longer to make sure her eyes came back down for a bit before they went back up again, and they did. So then I just relaxed more and let my eyes go back as well.
Then came the Vicks Vapour Rub. I put some under her nose and then under mine. Then we each took turns holding the vicks cup/container under our noses, inhaling deep, then exhaling through the nose into the cup/container so the "fumes/scent" of the vicks would bounce back into our eyes. And of course that was just...god damn. GOD DAMN. NEVER EVER BEEN THAT HIGH BEFORE IN MY LIFE. AND HAVEN'T SINCE. That was literally one of the best birthday's I've ever had in my life. And I was glad I had a girl at the time that was DOWN to do just about all of it with me. Needless to say the rest of the night was filled with more weed, cigs, and lots of sex. There's nothing like eating out your girl when you're both that high and she's doing full body twitches the whole time because of orgasm after orgasm was coming.
Maybe I'll have one of those days again. Or maybe I won't. I wouldn't want to spoil that initial experience you know? What I mean is, back then...which was...2005ish? Drugs were proper around here. I had connections that I now look back on and say "damn, I was THAT LUCKY when I was only 16!?" Nowadays...there's so much cut and drop in the quality that I fear if I try to repeat that experience I would be disappointed - well, not with the shrooms, weed, or the nitrous - cuz that shit is like 99% guaranteed to be proper quality. However the MDMA, and K (which in my opinion were the two heavy weights in that experience) have changed drastically. It's hit and miss now. Well I should only say that's true for small/personal amounts. If I went bulk I wouldn't have a doubt in my mind about the quality. But shit I'm not a teenager anymore, wtf do I need bulk for? You get what I mean?
One more thing to add. Minus that combo I just listed, the HIGHEST I've been off of ONE drug has got to be when I was smoking crack. Straight up. There has never ever been one drug that I took ONE HIT FROM that made me stumble, grab the wall, then grab my chest and say "holy shit I need to sit the fuck down" and then I held my ears due to the extreme ringing. That shit is fucking intense man. Honestly if that stuff lasted longer than 5 - 10mins....man...I think crack would be MASSIVE problem. Just imagine a crack high lasting as long as a meth high...my god..