Question about a scary experience with mdma

A couple months ago I did mdma on my birthday and I ended up having one of the most terrifying experiences of life. I had thought it was serotonin syndrome from now to since it happened, but after explaining it to some friends today, they and I are unsure about exactly what happened and I'd just like to know since Google isn't really helping

Leading up to that night, I had essentially been abusing Molly, doing it every month to 2 weeks, and doing heavy doses + redosing multiple each times each time and without supplements. I knew what I was doing was bad for me, but I had convinced myself that I could get away with it and knew this wasn't a habit I was going to keep up. This lasted around 6 months with the last day being my birthday this past March, which I had also planned before hand to be my final day before taking a extended break.

I hadn't taken mdma for around a month before the night of my birthday. I started with an initial dose of 1.5gs also took LSD and shrooms with it and was fine for the first 2 hours or so, but I then decided redose. I usually do up all my doses before I take my first dose but hadn't that night, so I went to go weigh some up only to realize the scale had run out of batteries. I then decided to eyeball my dose so I have no idea exactly how much I did but I know it was a lot. Then around 5 minutes after taking it, I went from feeling the Molly to feeling the high quickly begin to drain from my body until there was nothing left. It was so sudden and scary I had no idea what was happening to me. Everything was getting dark and I started panicking and it happened in a matter of seconds. At first I reminded myself that I was also on psychedelics and that this was just part of the trip, but I quickly went back to panicking as I knew something wasn't right about this. I had done mdma so many times before, done it with psychedelics so many times before, and nothing like this this had ever happen to me. This was never a way I thought I could possibly feel while on mdma. I was cold and shivering, it felt like my vision was getting dark, text on my phone became small and hard to read and I thought I was dying. It was like the hardest mdma comedown/crash I had ever felt and I was completely terrified. All I could think to do was focus on breathing and keep moving around to keep blood flowing through my body (no idea if that would actually help but it's all I could think to do). I eventually went to a friend and explained to him what was going on. He told me that I had just taken too much and stayed with me for the rest of the night. For the next hour I was experiencing nothing but terror. Just the absolute worst feeling I have ever felt in my life. But after that hour had passed I felt substantially better. I was having conversations, laughing with my friends, still kinda felt like shit but a lot better then what was feeling before. For maybe a around a month after it happened my mood felt a bit off, but from then till today I feeling completely fine.

Since then I've continued using drugs recreationally but not abusing them. Ive done LSD a couple times and with shrooms once and felt completely fine throughout the trips. I'm pretty scared to try mdma again after this experience tho with the fear of something like this happening again or worse, but at this point I'd just like to know if this was actually serotonin syndrome or something else, since whenever I look up the symptoms, while some things match up, it doesn't seem to match up exactly

Thanks for reading Looking forward to read any helpful replys :)