Forgetting a whole song

I went on stage yesterday in front of a teeny crowd of about 20 people. We were playing four songs. The first one went well - started playing the second one and... couldn't believe it... as the vocals were due to come in I realised i couldn't remember the words. Played the chord pattern a couple more times while Tom looked increasingly concerned then started singing some nonsense words and basically just making it up as I went along.

Making it up as you go along is far more convincing when you are playing on your own - you can't really just make stuff up when two of you are playing because the other person starts to freak out and doesn't know what you are doing.

The only other time I remember anything like this happening is in a band I used to be in where the bass player after we'd rehearsed for 3 months got up on stage and forgot all the songs. With him I think it was nerves - with me I'm not sure what it was - possibly nerves - I'm used to playing acoustic sets on my own and not with another person and this time there was all this added pressure to 'stick to the plan' and on top of that we were playing a song I'd never done live even though it's on the album so I've probably heard it a million times.

Is it age? At age 28 do I have musical dementia? And what's the cure? More live performances? Does this not just create the likelihood that I will forget more songs in front of even more people?

Help!