I don't see why the mere act of clearing your mind for a few minutes would be sinful. I think some people mistake it for an act of prayer because they look very similar, and under some religions meditation does end up taking the place of prayer, but it really depends on what you're doing. If you are meditating in the sense of clearing your mind for a few minutes then it seems fairly impossible for that to be a problem. If you're praying to buddha, well maybe you shouldn't do that if you're a Christian.

I believe there have been clinical studies on the effects of meditation, and the general effect is an increase in mindfulness. That is, it takes you out of all of the other things that are going on and helps you focus on what's going on in front of you right now.

On that being said, a sudden change in your ability to stay on task could indicate some other change in your life. The ability to regulate attention is generally consistent, so did something happen to change your ability to regulate attention? Did a change in your life happen, has something been bothering you, have you had something on your mind that is particularly bothering you? We live in some very stressful times so it's understandable, but if you can better understand what is bothering you you might be able to take some steps to alleviate that bother. All the things that we have are giant brain for are about trying to predict the future and in a sense recieve prophecy so that we can do something about it before it becomes a problem. The level of prediction and planning in our brains is completely on another level compared to any other animal. If your brain is warning you that something is going to become a problem and you're ignoring it, in an allegorical sense it's like ignoring prophecy, and throughout history it has always been considered folly to ignore that kind of prophecy.