yes, I have proof that anxiety is caused by low blood volume (hypovolemia). Just do a google search on your own and you can find plenty of information.
Google search: "Hypovolemia anxiety"
Google search: "Hypovolemia cfs"
You will see that hypovolemia is a main symptom of chronic fatigue syndrome (which most of us on this site all have in some sort of stage).
I haven't really looked into it much, but I remember reading that hypovolemia happens due to infection.