Has anyone here studying with any CBT product and start getting sleepy?

I found this to be true when studying for Sec+ and now 70-290. I also find that the time of day I view these is an important factor. After a good 8-9 hour day, I come home and try to study with a CBT product and next thing I know im out like a light.
Its not that i find the material boring or un-interesting. For some reason they just sometimes put me in a hypnotic state and I fall asleep. Usually after a good 30 minute nap, however, I can view them for hours on end.
Im convinced that CBT products have the same chemical as Turkey