What Causes High BP,fatigue,dizziness And Shortness Of Breath?

My sister is experiencing occasional episodes of dizziness, extreme fatigue, sweating, shortness of breath, and nausea. The onset has been sudden and lasts from several minutes to hours, though she says she has been feeling unwell in general for several months. In the episode I witnessed 2 months ago, we took her to the hospital. Her BP was very high (150 s over high 90 s) and she listed to one side when walking. She commented that she didn t feel right in her head and that it took effort for her to speak. There was no blurred vision, or noticeable speech difficulty. The ECG, MRI , and all lab work were normal. Her family physician has been unable to identify the cause and she is not being treated. Her BP is usually normal at the doctor s office, but she did a self check (at pharmacy) when last episode occurred and it was again in the 150 s to high 90 s. I m concerned something is seriously wrong. Suggestions?