Why was Dorothy Assex suddenly desperate to go to the bathroom?

Well, it was because Alex Rockefeller used his Chi that had healing properties to force the drug out of her body through urination.

Thus, his treatment effectively stimulated her need to use the bathroom.

Alex picked her up and walked out the office.

When Anderson Assex saw them leaving, he immediately crawled over to pick up the signed contract. He wanted to hide it.

As long as he acquired the contract, it would be worth it