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So much for flame free forum announcement when you enter the forum.
I doubt that there is a single brand and model of dive computer that has not failed at one time or another (not battery failure). I personally have had 3 or 4 fail over the past 22 years I have used dive computers. The thing is, you need to be able to recognise and react to that failure. While the OP recognised it, he did not react to it in a manner that indicated enough knowledge to be doing that sort of dive.
Some comments have been made about doing decompression dives using the computer when the manual says not to. Many computers have this standard statement to presumably remove the chance of being sued later on.
The things that are not clear to me is why you started the dive with a tank that was nowhere near full, why you did not just backtrack the way you descended and then spend as much time as possible at 3-5 metres (10 to 18 feet) till your air was almost expended. This is one of the most basic of all things to know if you do a dive where you have probably entered into decompression.
Sheez, so much for flame free forum announcement when you enter the forum. The blog was written well before I posted about it here. I've certainly read all the posts here very carefully and clearly understand them. I did learn a lot and I will continue my training beyond its current level. My next dive will be #239, the number is correct. Some people dive or do whatever they enjoy all their lives without incident, some people can't get past the first couple times of trying a sport before they come across a major hurdle. They can either give up or learn to deal with challenges, failures, etc. I choose to learn, I don't give up.
I also learned more here than from all the casual observers that read my blog so inspite of the pounding I'm glad I posted here. I get it, I get it, I get it. OK.
The tank is a LP 125 and is full at 2400psi. I started with just over 2500. I did backtrack following the sloping terrain in the opposite of what I descended. Agreed, one of my mistakes was I didn't keep going until 10-18 ft. I had enough air to get there and did not think that through as I should have. Even if I didn't know my exact depth I should have kept on going shallower since I was low but not out.
I would like to amplify SuperLyte27's comments on narcosis. You said you were not narced. I assure you that you were.
I have no trouble believing you could have gone from 150' to 220' feet without any memory of doing so, even though you felt perfectly fine and clear headed when you did it.