This is not an isolated occurrence; I often find my thoughts drifting at times in church and have to pull my attention back to what is going on. I have even caught myself in mid prayer (mid song even) starting to lose my attention or even completely forgetting what I had just said (or sung). The hardest times are when, like today, I am tired to begin with and find myself easily entering into an almost dreamlike state.
I only go to church once a week and only for a little over an hour. That is such a small portion of my life; why dan't I give my attention more fully to God? But this isn't just true of God, there are many aspects of my life that deserve greater attention (especially my wife and children) yet end up being drowned out by problems, dreams, and stray thoughts. I need to learn to give attention to those things that are truly important in my life, but I also shouldn't beat myself up over my lack of attention.
I am human, and my attention wanders. As long as I work to bring my attention back, as long as I don't forget what is truly important, I can forgive myself those lapses.
I have since read the second reading (and found my attention wandering again, but I pulled it back) and noticed that a portion (Romans 5:3-5) actually talks about something similar to my earlier post on suffering. I really should pay better attention.