I was diagnosed with below average intelligence after a mental exam in a hospital. does it mean this is my permanent iq or my iq during this time?

Hard to say: IQ tests were originally designed to predict performance in academic pursuits. Since "average" is assigned to an IQ of 100, you could be considered below average if 99, although it would not use the label until you were 15 points down. You can always under-perform on such tests due to transient conditions. If you were in a state of good health it is likely how you would always function.