“Therefore do not worry about tomorrow, for tomorrow will worry about itself. Each day has enough trouble of its own.”

Should I feel guilty for the times in my life when I have been unable to sleep due to an overwhelming concern that takes over my thoughts regardless of how I may try to “not worry”? When I see someone who is completely unprepared for a known event, I think of how I could not live like that.

In this life we have many God-given responsibilities, especially to our immediate family, to provide and care for them, and to people who rely on us at work and church and amongst our friends. Does this verse mean we are not to concern ourselves with them?
I think the key here is that verse 25 begins, “Therefore I tell you, do not worry…”, i.e. it follows directly from what has gone before in verses 19 to 24, which say, “Do not store up for yourselves treasures on earth … But store up for yourselves treasures in heaven … You cannot serve both God and money.”
From this we see that the worry Jesus is talking of results from allowing earthly concerns and things to become our treasures, or our gods. To make gods of things that God has provided only for temporary use, that are here today and gone tomorrow, is bound to cause us pointless distress.

The earthly responsibilities we should concern ourselves with are those that God has given. But as He also provides the material resources and skills to fulfil those responsibilities (such as patience and understanding, clothing, food, aptitude and qualifications), so that concern need not become fear.
And the need for those material possessions and skills is only temporary.

This verse reminds me of the manna given in the wilderness to the people of Israel. They were told to only collect enough for the one day, and to rely on God to provide enough for each day. And if they accumulated more than was needed for the day, it only became bitter. And so it is with us today in what God provides.

I think we are meant to do all that is within the resources or power given by God to fulfil those responsibilities He has given, which may involve planning and careful attention to detail. To do less is to rebel against our calling by God. And He may disturb our sleep in the early hours to alert us to all He wants us to do.
But if we make gods of what He equips us with, including clothes, food, and shelter etc, and our lives revolve around those instead of the one true God, we are bringing calamity upon ourselves.