If you can intentionally create doubt, you can also release it.
People say “I have doubts” or “I wish I could overcome my doubts” but have taken little time to actually examine what doubt is. It’s split-attention from holding two incompatible thoughts in mind. The word doubt comes from the root “two”.
To get rid of the doubt you choose one of the two conflicting thoughts and withdraw attention from the other, or choose a third thought that is more easy to believe or combines/integrates the two or focus on things you are certain of.
Doubt, by the way, is not a bad thing. It helps you clarify your thoughts and direction. If you say “I can jump off this building and not get hurt” and you have doubts, your doubts are saving your life, telling you that you need to choose thoughts more in line with reality or with what you already believe.
Anxiety is from making a thing more important than it is. If you feel anxious on a date, you’re making your date more important than he or she is. If you feel anxious about an exam it’s because the exam looks bigger than you instead of you bigger than it. If you feel at level 5 then anything you label a 6 or 7, makes you feel inadequate or anxious. To reduce anxiety you need to reduce the importance of a thing. You can do this by reducing the labels, judgements, expectations, etc.
If you assign too much positive to something, you could use negative labels, if you assign too much negative to something you could use positive labels to neutralize the energy. Splashing cold water over your face also does the trick (reducing anxiety is always a matter of cooling down).
Another way to reduce anxiety is to reduce the level of challenge you are putting yourself through.
In some cases, anxiety can dissolve if you relabel the sensation “excitement”.
Calm can be produced quickly by focusing on one thing. Or by calmer breathing. By extroverting attention. And many other ways.
Investing time into dealing with anxiety and calm – what triggers it in you and how to stop it – is extremely worthwhile.