What Causes Severe Anxiety And Breathlessness While Being Diagnosed With MS?

My boyfriend has MS....the relapsing, remitting type. He just had pneumonia and went into hospital twice...first time because of trouble breathing and his MS they think exacerbated making him so weak. The second visit a few days later was because he was having severe anxiety from the rales and creaking sounds coming from his chest. The third visit was because after a clear chest xray , and doing well, he all of a sudden was very weak and dizzy in the morning. He slept all day and when I visited him, he was having trouble finding words to complete his thoughts and he was confused. He was also very weak a very shaky. Took him 5 seconds to tell me the month we were in. They did a CT scan and MRI and all was clear. No indication of stroke, so they attributed it all to an MS attack even though the MRI was clear. We have an appt. with his own neurologist tomorrow. Why is he having this type of speech/thought process/weakness/shaky problems if the MRI is clear. I read that acute aphasia is very uncommon with MS patients. Could he have had a TIA that was undetected and without any of the classic stroke symptoms present?