Panic attack at 11m

So yesterday we go up early for a dive at Terrigal, on the New South Wales central coast. I was feeling a tiny bit nervous because of the dive I had to abort in Chile because I couldn't equalise, but otherwise I wasn't thinking much. We got to Terrigal, signed our release forms, set up our gear and headed out on a bumpy boat ride to a "reef" (not a great barrier reef style thing, more of rocks with kelp). I had taken antihistamines and used an antihistamine nasal spray to make sure all my mucous membranes were nice and shrunken to help with equalisation.

Just before we set off I said to Brandon, "You know in the Galapagos, when I was 6m above the rest of you, that was pretty dangerous because if I had panicked I would have drowned." He just shrugged it off and it was just a passing comment.
Everything seemed pretty rushed and we were out of the boat and starting to descend before I had properly caught my breath from getting geared up. Which was probably the first mistake I made. We were headed down straight to about 13m and so followed the anchor line, me bringing up the rear as usual as I slowly equalised at just about every 50cm. It's the first time it has really bothered me that I am always last and everyone is generally at the bottom waiting for me. Everyone else pretty much dropped like stones compared to me. My ears cooperated and I can say this is the first time I haven't bruised them at all. My mask was fogging and I tried to fill it with water and clear it again a few times before I gave up because I was swallowing air trying to clear it. We neared a rock shelf and everyone else let go of the anchor line and dropped down. So I let go too and dropped down 50cm or a metre and had to come back up because my ears were being difficult. I put a little air in my BCD (a vest that holds your oxygen tank, weights and is inflated for floatation and to adjust buoyancy underwater), but not enough and had to fight to stay at the right depth while trying to equalise and clear a little bit of water from my mask. I had read that having a clear mask helps with equalisation. There were a lot of things running through my head. I added a bit more air to my BCD. Still not enough. My legs were tired from treading water. Suddenly I just couldn't get enough air, the water was closing in around me and crushing me. I tried to breath slowly and deeply but there still wasn't enough air in my BCD to stay at the right depth, I sank and my ears pained. I struggled to get back high enough to relieve the pain and thought "if only I can grab hold of Brandon I will be able to calm myself down enough". But he was too far away to reach in the next 10seconds. He turned away and I desperately gave him the signal that I needed to go up but he didn't see and turned away from me and started swimming away. At this point I knew there was absolutely nothing on the planet that would stop the panic and if I didn't start ascending I was going to rip the regulator from my mouth and make a bolt for the surface. One of the biggest mistakes (and often fatal or seriously injurious) mistakes a diver can make. I started moving towards the others again and the dive master turned and I furiously signalled to go up. He was over in a minute grabbed my hand and we started ascending. The panic was so intense by this stage I couldn't even think to try and slow my breathing. He stopped when we reached what I imagine was about 5m and asked if I was ok. No, I really wasn't and if we were going to stay here any longer I was going to force my way to the surface. The whole way up I had been reefing at the anchor line while he held me back to slow the ascent. I knew what he was doing and that I should stop trying to force my way up. But it was proper panic and all I wanted was to get out of the suffocating ocean. When we got to the surface I grabbed the boat and he headed back to the others. Perhaps the panic was less when I could breath air but I was still feeling like the life was being crushed from me. It was a struggle to remove my fins and climb aboard and it was only after I was out of the water that the panic subsided.
I can honestly say this was the most frightening experience of my life. Your brain is divided: one half is screaming to just get out while the other is telling you that's a good way to die. Which is not all that calming. I know I could have drowned. Plenty of more experienced divers than me have drowned because of panic. You never know how you are going to react when you panic until it happens and I'm glad I was able to signal my panic without doing anything stupid. Maybe it's because I have read many, many diving horror stories about deaths that could have been avoided.
I had a good half hour in the boat to think over what happened and I still can't figure it out completely. We have been diving is horrible visibility and in situations where I am a good few metres above everyone else and I have been fine. I have done boat dives before, where you follow an anchor line down. And I have never experienced any kind of claustrophobia before. My hesitation at future dives is pretty well founded, but I will definitely dive again. And if it happens again, I will grab back onto the anchor line and pretend nothing exists but my breathing.