Thanks for all your messages - things have improved slightly but it is very tiring. It is so difficult to know what to do. Leaving her crying just seems so heartless and I know a lot of people on Mumsnet do not like controlled crying, but then if we sit with her it could go on for weeks!
Last night I spied on her through the crack in the door, there was nothing happening in her bedroom at all (I was beginning to think it must be haunted!), she was simply pacing the cot, stopping every now and then to scream at the door and cry 'mummy, mummy gone, mummy' which was heartbreaking to hear. She would snuffle her teddy for a bit and then start again. Eventually I went in to tuck her in and out of impulse I moved a dressing gown that was hung on the door and has been for months (we had been through her room previously looking for anything that might be spooking her). After I had shut the door she continued crying for about 5 minutes and then just stopped! She did wake up in the night for about 10 minutes but then settled herself to sleep again. I don't know if it was just co-incidence or not.
Like yourself Art, mine was a perfect GF baby too, this phase just started very suddenly. I would look round his room and remove anything that might spook him, even if it looks innocent enough to you. I don't know if you can do the controlled crying thing, but sometimes it is the only thing to do, otherwise it becomes a habit and your ds will not be able to go to sleep without you being in the room with him. All I can say is that it does get easier, the first night of crying is the worst, but after that it does get better.
Call someone whilst he is crying to get some moral support, my sister talked me through it the first night, I was sobbing on the phone as I listened to her screaming, but I'm glad I kept my resolve. It didn't affect her mood the next day, she probably doesn't even remember it.
Anyway, I have to try and put her down for her afternoon nap yet so I'm not holding my breath that things will be ok. Thanks for the support though, and I hope things work out for you Art, let us know. I'll be thinking of you.