I took the PADI deep course a few years ago from what I consider to be a very good PADI instructor. He taught the course to standards and a little above but in all honesty looking back now from my own view as an instructor and someone who has taken a bit of tech training the course was not thorough enough.
There was a great deal of info lacking in it. Not enough time is spent on equipment configuration and selection of the gear and why. Emergency deco procedures are IMO glossed over and the hazards of going into deco and the hazards of deep diving itself not emphasized enough. Actual deep diving should promote some anxiety and in some cases enough that that certain divers will just reconsider the whole idea and not do it. Emergency deco procedures should be part of any deep dive and planned for as back up. The problem is that the instructor may not have a good idea of just what those procedures and tables are. When choosing a deep instructor ask them what tables they follow for an emergency deco event. If they say the RDP guidelines - run like hell and find someone else. I use either v- planner, the US Navy Deco schedule, or the emergency deco tables we teach in the SEI Open Water class. Try to find an instructor that has a track record of deep diving ; preferably technical deep dives. Their idea of planning and actually executing those dives usually carries over into the ones they do recreationally.
I also do not think that 4 dives is enough - I'd like to see 6 over three days min- and the min depth for those dives at 80 feet. With at least three of them in excess of 100. 3 dives to 70 -90 feet and one to 110 is not enough experience. Also the required skills on those dives are a joke. there are no real task loading skills other than a timed task at depth - mine was a combination lock. I have students run a line and reel at 90-100 feet in my AOW deep dive, perform air shares, and communication exercises at that depth. In a deep class they would also perform buddy breathing, gear removal and replacement, switching to a stage bottle as a planned and as an emergency exercise, and a few other things I would come up with based on their needs and reasons for diving deep. I might have them recover a concrete block with a lift bag and bring it from 90 to the surface under control.
In the course they also talk about optional equipment for deep dives and what they consider optional I do not. Every item is essential including a proper redundant air supply, lights, reels, emergency O2, and back up gauges. I also consider a lift bag and /or SMB with reel or spool to be required gear. And deploying that bag from a depth of 80-100 feet should also be an exercise in the course.
There also needs to be enough face to face time in the classroom with the instructor and while self study is valuable it should supplement the classroom not replace it.
I'd also advise you to not rule out a quarry for training. Not all are the same. Gilboa with it's 40 degree bottom temps will be far more challenging than a warm water dive to the same depth and test you more. You may not have the currents but it will not be an easy walk in the park.
Management of narcosis is possible and there are a number or ways to do it. I have my own method that for reasons of liability I will not detail here in fear that someone may try it and get hurt by misinterpreting what I use and then sue me or worse their survivors sue me. I will only say that it involves task loading myself in a set manner during the dive to stay alert and aware.
The best way to manage it if you are going to do deep dives is to eliminate it. I like Helium for that
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In short do not take lightly what you experienced and don't take a deep course just for the card. Find a course and an instructor that will give you an education and don't limit yourself to any agency. Interview the instructor and the shop if going thru one like you would if you were hiring an employee to train your most loved family members. I have three chapters in my book dealing with interviewing an instructor, interviewing a shop, and deciding what training is best for you and when.
I have been told it has saved some readers money, time, and helped them get better training by knowing what questions to ask.