It can be a side effect of lexapro but it could be a side effect of chemo or even the after effect of lorezepam. Are you drinking plenty of fluids...like 2 litres a day? I got very dizzy if I stood for long on AC chemo, more so week 2, my BP was very low apparently.
Probably wise to stay on half until you see your Dr. It will reduce anxiety but does take time. You may benefit having either a referral to a mental health clinician through your Dr or your local hospital would have services. They could teach you some relaxation techniques that will reduce anxiety and also help you sleep.
Apps you can try are "Smiling minds" or "mindshift". There are some self help tools in there. ..just Google and you will find them.
Reading to empty your mind. Reducing coffee, cigarettes, cola later in the day. All these things can help.
Feeling stressed, anxious, frightened with a mind that is constantly thinking is very normal following diagnosis and treatment. But there are things that will help.
Hope things improve for you soon. Kath x