This isn’t an uncommonn situation though. The old rhetoric about the fear of death being second only to public speaking isn’t just a saying. That fear of being the one on stage under the spotlight, being singled out from the group and put under pressure, it isn’t something that goes away with practice. You get used to it, but that fear is still always there. Don’t let that scare you away from speaking though - it’s extremely fulfilling, but it’s still scary. So is jumping out of a perfectly good airplane, but people do it.
If I could give just a few hints about what I think help can help with nerves for speakers:
for goodness sake, get a good night sleep before hand - speaking hungover or tired is not fun.
if available, remove yourself to a quiet room before hand and do whatever you need to psych yourself up. Don’t worry about trying to see the talk before yours - they will probably be recorded, or you can ask about the topic later.
if you feel that you are unable to present - let someone know. It’s ok to know your own limits and back out.
And for conference organsisers - I know conferences are hard to organise, but your main attactions are your speakers, and you need to take care of them:
have a quiet room - somewhere speakers can sit in the quiet to prepare and relax
have backup speakers - The backups do need to understand that they are basically understudies - they may not get called up, but if they do, they should be ready to go.
if you do have a schedule change - please be careful in how you announce it. Change the online schedule, and gently tell the audience there’s been a change in the schedule. Please do not ever directly tell the crowd that someone ‘piked’ or ‘chickened out’. The original speaker will be in a very fragile state. They need support and comfort, not accusation.
make sure anyone who was ‘subbed’ out is OK. They are going to be in a less than optimal state, and should be treated with care. Ensure they have whatever support they want, and try not to overcrowd them. Someone who has just opted out of a social engagement may not be up for much social interaction at that point in time.
Update, August 2015: Through the support of a good friend of mine, I was able to present the black deck at a local meetup. It was good to be able to get it off my chest. A recording for this presentation will not be available, but the slides are.
I strongly suggest checking out BlueHackers and > Prompt for resources and advice on mental health specifically within the tech industry. If you need to talk to someone, LifeLine is always there to help, but if life is in danger, call emergency services.