Could Palpitations And Sweating Be Normal In A Child While Recovering From Stomach Virus?

Hi. My 7 year old son recently had a stomach virus. He threw up several times during the night and laid around most of the next day; which is normal behavior for him when hes sick. Later that evening he fell asleep on the couch aroud 7; at about 8:00 he woke completely freaking out. He thought there was a man in our living room, you could tell by where his eyes were looking that he thought he saw something. He was terrified, his heart was racing and he dripping with sweat; at one point he asked if he was going to live. This behavior of course scared me and my husband. He did not even have a fever at that time. It took a good 10 minutes for him to finally snap out of it. We called his doctor, she said to take him to ER to make sure he was not overly dehydrated. There they said he did not show signs of dehydration but his bloodwork did show an infection which was likely viral and we were released with no medication. The next night he had the same episode. His dr said its from being so exhaused from the virus and that kind of crazy talk is not uncommon. Hes better now, still not back to his energetic self though. We are still worried about the episodes that he had. Is that really normal ? How do we know if there isnt something going on neurologically?