@comfyshoes - I agree. I've had a lack of sleep over the last few nights which has caused me to yawn more.
I'm finding that when I try to interpret something at work which I do not understand or does not interest me I'm yawning more.
However, upon engaging my brain in a couple of games of checkers, looking up this site, and writing this post, I've not yawned once even though I'm thinking and writing about yawning.
Prior to writing this I thought I couldn't stay awake because I was so tired and yawning so often but I feel OK now because my concentration and level of interest has risen in the last 15 minutes.