Have you ever settled to pray in the evening and had trouble keeping your focus? Most of the time I pray in my head, that is to say that I don’t actually use my voice. Somehow, even in my own bedroom at home, praying out loud makes me self-conscious. This isn’t an issue for me in worship or anytime I’m praying with others.
Worry about seeming silly if my kids or husband come along and hear me is only a part of my problem. It seems that when I voice my private prayers they hit me more deeply. I almost always end up crying at some point. Similarly potentially embarrassing, this is an emotionally exhausting experience. I suspect that the tears etc actually are some indication of the value or efficacy of the prayer.
In the end I don’t know if it matters whether we pray in silence or aloud, but if you find yourself wandering off to plans and worries about the next day try switching. Maybe the sound of your voice will keep you on track.