Hello, I Am A 43 Year Old Healthy Female. I

Hello,
I am a 43 year old healthy female. I saw my doctor today because I've been struggling with anxiety for the past three months. Heart racing and palpitations and sometimes my old pressure stays normal, but sometimes goes up. (On thyroid meds and all numbers check out, hormones in range too).
I drove myself to the hospital a week ago because I was having a panic attack after racing heart all night. My blood pressure was up to 160/101. They tested my heart and ran blood tests and everything was normal. So the gave me two Zanax and three baby aspirin and my BP and pulse went back to normal, blood pressure was once again 122/80.
At a follow up appointment my doctor gave me a sample of Bystolic today to try for the anxiety. My blood pressure went from its normal 120/80ish to white coat syndrome today138/94. I have been fearful, sleep deprived and very nervous about going to the doctor.
I took 10mg of Bystolic today. I have read of so many negative side effects and negative reviews on Bystolic.
Now I'm afraid I should have started at 5mg. Not 10 mg. I'm afraid I might get such low blood pressure I might die in the night. Could that happen on 10mg since my blood pressure is usually normal?
Also, if I'm not comfortable with this medication can I stop taking it tomorrow or do I have to GRADUALLY decrease it after taking it once today at 10 mg.?
Thank you so much!
Andrea