Good Morning Gem,
I am sorry to hear you were feeling good and then whammy, yes that happens to me way to often and it has taken a lot of practice to learn how to pull out of the anxiety spiral as well as to accept that I am a person with anxiety.
When looking at the topic of anxiety there are a couple of terms known as Specific and Non-Specific Anxiety.
In the majority of cases of clinical anxiety, the fearful feelings are fixated on a specific threat: an identifiable person, activity, event, or circumstance. This type of anxiety is therefore known as "specific anxiety." The phobias would fall into this type of anxiety.
On the other hand, non-specific anxiety -- fears that are not easily attributed to any particular source or trigger -- are often more disturbing and more difficult to manage clinically. This type of anxiety is called "free-floating anxiety" when the anxious feelings occur spontaneously and without any apparent cause.
I believe that I have more non-specific anxiety as I will have days where I just burst into tears of anxiety and cannot identify why I am feeling so anxious. One of the things that helps me to pull back from the anxiety is music. Listening to music which is soothing will help to redirect your immediate thoughts away from any anxiety you feel. The calmer the music the more effective it will be towards soothing your emotions. Even if you are a hard rock or rap fan you will still appreciate and benefit from this type of music.
Take care and remember to keep on moving forward, one babystep at a time.
Hugs
Kitt