Final answer:
The described symptoms and behaviors of the patient are indicative of Panic Disorder with Agoraphobia, a condition characterized by recurrent panic attacks and avoidance of situations where escape might be difficult.
Step-by-step explanation:
The most likely diagnosis for the 30-year-old female lawyer who experiences a racing heart, shortness of breath, chest tightness, dizziness, blurred vision, fear of death, trembling, and sweating in an elevator, and who has started avoiding it due to her symptoms, is a) Panic Disorder with Agoraphobia. These symptoms align well with documented cases of panic disorder, which can entail intense episodes of fear along with physical symptoms that are not attributed to any other health issues. Avoidance behavior, such as choosing to walk down 20 flights of stairs to avoid triggering episodes, is a common manifestation of agoraphobia which often accompanies panic disorder.