Feeling Stressed

I have become very anxious these days. Last week, I secured a role and received confirmation from the employer, who requested my documents. After a few days, they called me with an offer that was 20% lower than my previously communicated expectations. Obviously, I tried to negotiate, but I haven't received a response from them in four working days. The HR representative says they haven't gotten approval yet.

It is a reputed product-based company, and this is an offer one cannot neglect. I can envision a compatible future with this company. What can I do now?