Scary experience while diving today

What a scary experience while diving today! I guess I went very close to a fatal accident! I premise that Jennifer almost forced me to take the open water diving course because she is already a professional diver so she would like to bring me to Philippines for some underwater time together. I am a professional swimmer so I love the marine environment and I am very attracted by the water world, but at the same time I consider exploring it very unnatural and dangerous. I mean, if I think about having to use a tank, paying attention at gauges and being careful about not going up or down too quickly, it gives me the idea of being so powerless down there… Anyway, I wanted to challenge myself again and as usual I pushed myself over the limits so here it comes my scary experience: I am on my second dive of the day, the nitrogen level in my blood accumulated during the first dive is maybe still high, we are a group of 4 people and I am the last one, we are about 18-19 meters, the view is marvelous, the coral reef and its inhabitants look amazing, at some point I see a huge sting-ray passing very close to me and descending slowly: she looks friendly so I cannot resist the idea of swimming and touching her, so I start to follow her, but forgetting to inform the other divers about my intentions. I then descend few more meters but when I get close to the sting-ray, she accelerates her swim and in a matter of seconds I loose sight of the animal while suddenly starting to feel disorientated. I feel my head heavy and my brain turning upside down, I try to have a look at my diging watch which is indicating that I’ve gone over the depth limit, but my residual air is more than enough (around 90 bar), however I look up to search for my other buddies, but I’m unable to locate them. After few seconds I also start to feel weak and my heart is beating so fast, I’m scared to fall unconscious… I feel cold… I want to escape from this trap, run up and finish my dive but I’m also scared to have a lung overexpansion if I ascend to fast. So I inflate my buoyancy-control-device (BCD) to a few bar, this way I will be pushed up without having to move too much and just after ascending about 5 meters I feel my pulse was lowering and the dive instructor right on top of me. Nobody seems to have noticed my absence and I start to wonder how long did all this really lasted even if I felt I lost sight of everyone for at least 5 minutes. Anyway I am about to tap the instructor to let him know that there was something wrong, but all my faintnesses are slowly disappearing so I decide to wait a minute before giving the alarm, I’m not feeling well, I feel a very strong headhake and pressure on my ears. I try to re-equalize, forcing my jaw as well, and it seems it’s getting better. So I normally finish the dive at about 15mt deep. My brain starts to work normally and begin think what I did wrong… Could it be nitrogen narcosis or Co2 toxicity ?? I dont have a clue, I’m just a beginner at his 5th dive, anyway I do my 5 minutes of safety decompression stop at 5 meters, still scared and anxious to be taken by an embolism attack at the last second. Soon later I cant believe I’m out of the water, safe and breathing fresh air. I inform the dive master about what just happened, and he says my accident might have been brought by a missed step on equalizing the pressure in my ears while descending… however I suspect it might have been an axiety or a panick attack underwater…