While I'm sure there are people who can focus on fishing 100% for hours at a time, I'm not one of them. Fortunately, fishing doesn't require focus, since it's so simple. Turn on the TV, read a book, browse the Internet, do some cooking - whatever you like to occupy yourself while you're fishing. The only time you need to pay any attention is when you get a mooch fish, and that's only if your Big Fish requires mooching. Otherwise, just cast, catch, cast, catch... Easy to do while reading, or whatever.

To me, it's no surprise if you get drowsy after 10 minutes of fishing - so be sure to do something OTHER than fishing while fishing, to prevent the boredom from setting in.