Hand Quilting Stitch Blindness
 

I can't think of a better description, but I wonder has anyone on this board experienced this. I find that when I have spent many hours hand quilting quite happily and systematically, I suddenly lose the momentum and I am unable to gauge the size of the stitch I am using. I have to put the work away for a while. I hope there is a rational explanation for this and I am not losing my marbles.

You may be approaching burn out. You already know the solution because you are doing it!

Whether machine or hand quilting, I think that when you've worked very long on it, your eyes do get tired and your mind tends to get bored and start wondering. You just need to take a break!

when I begin having trouble with my stitches, I take it as a sign to stop for the moment, and do something else. When I go back to it later, it's fine.

Oh, that's a relief to know it is not uncommon. I will take more breaks.

I hand quilt also and when I feel like it isn't going as good as it should or I am getting tired I just quit for a awhile
maybe until the next day. You aren't doing you quilting any good by quilting when you body and mind aren't into it.
don't give up just keep quilting when you are in the mood.
bigsky

I actually did research on the topic for learning in another area that I was working in. Studies have shown that the brain works at optimal performance for twenty minutes.then starts to slow down or wander. Push too hard and it will rebel. ( my words not the scientific jargon. :).)
You are doing the right thing. The studies agreed that simply take a five minute break every twenty minutes to get optimal performance results.
Just change your focus, drink some tea, design a different pattern or maybe read an article.
You are doing fine it's not a problem it's very normal and it demonstrates that actually you are functioning well.
So go ahead and enjoy your long sessions just add in even more. LOL.

just take a break for a while.....

As others have said, take frequent breaks. Get up and walk around; give your brain a rest and your eyes a break and focus on something else. Good luck and happy quilting.