One day fever

Earlier in the week Jakob woke up at midnight one night with a high temperature. The next day was the same, he was very hot and tired with a temperature between 39-40 degrees. We stayed home all day and he spent most of it on the couch either being very hot or feeling very cold. I was very surprised that he woke up the morning after with no temperature and feeling good! I felt like a bad mum when taking him to dagis (he asked me the whole morning from 6-9 if he could go) but he was exactly like normal all day and didn't even seem tired in the evening. Strange sickness. To be so sick one day and so well the next day.