what the bad consequence would be after long time fast heartbeat

I recently stressed out due to a new job, and diaglosed with anxiety in ER, the ER doctor wanted me to take Ativan, 1 pill 1mg once every 8 hours. I am afraid of dependency if taking too  much, so I only take 1 pill at bedtime. I did get 5 to 6 hr sleep, and feel normal in the morning about 5 hours, then feel stressed again. My heartbeat is around 100 when I am stressed, and I feel my throat unconfortable
my questions are:
1. if I take the Ativan as the ER doctor suggested, in the day time, how can I work ?
2. long time fast heartbeat like 8 hours continuously, what bad consequence would happen?
3. what medication can be done to cure this anxity?

I am so afraid of this could cause me lose my job, please help.
(I can not type in Chinese with my computer, sorry for this)
Thank you.