Philippians 4:6 do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God.
Anxiety is that fear or panic of something not immediately confronted with, but is either off in the future or maybe only imagined. An example would be the fear of a test in a class you are not particularly fond of, but that is two weeks out.
Anxiety represents a recoil or reflexive defense that kicks in well ahead of any actual danger. This kind of fear becomes a problem when we are so afraid of the “possible” or imagined outcomes of the future that we do not act in our present life. This is what Paul seeks to release the Philippians from.
The future is unknown to us, which makes it somewhat scary. Paul’s (God’s) answer is to take all such concerns to God in prayer. Not just prayer for the future to work out to our benefit, but with a thankfulness that trusts our future to God. It not only vents our fear to God about the test, but thankfully trusts God with the outcome of that test, WHETHER GOOD OR BAD. Maybe your major hangs in the balance via the test you are anxious about, yet by failing it, God brings you to a point to change your major to a calling you will find more fulfilling and in line with certain gifts He is developing in you. We fret and squirm over some future event, imagined or real, thinking its outcome will make or break our future. Yet if Christ is our future, present and past, it is already made and you can plan but pray, “as the Lord wills”.
I know many Christians who say they would lay down their lives for Christ, but they don’t live, pray or act that way. If we really trust that God has the best plan, then I can and should do everything lawfully in my power to get better from a cold, but I should be open to the idea that I may be called to die. It could be that by death a friend or relative who would never come to a church, comes to the funeral and via your pastor’s service is introduced to Christ.
In short, take your cares to Christ, but trust to leave it and the outcome to Him as He has already provided us with the best possible future.