Robert, many thanks for your comments , I will take onboard advice.

You're not unusual (well, not in this respect, anyway!). I will do almost anything to avoid starting a painting, even though I've been at it since I was around 15, which is ... um .... some years ago now. What helps me - two things. One, I don't put pressure on myself to perform like a seal at the circus; I paint when I'm ready, and if I'm not ready, I don't paint. Two, I put a Mozart CD into the player: it nearly always works on whatever portion of my brain responds to these things. Doesn't have to be Mozart for anyone else, of course - could be the Elspeth Trembath Triangle Trio .... Don't punish yourself emotionally for not painting - you'll set up a neurosis! You're retired, I presume, have all the time in the world - just fit it into your new schedule when you can, and don't worry about missing a session or two. In your previous life, people were expecting you to perform and deliver the product - well, they aren't any more, that's all. The only one to please is yourself - but if it helps, imagine yourself as the office junior performing for a demanding boss. I don't say I recommend this at all, because that's the life I was glad to get away from - but whatever works for you, is the point.