From which vaccine? There are a number of vaccines, and it is expected for the body to "fall ill" a bit since the anti-bodies are being built. This is usually the case with all vaccines in general. I was an infact when I had received the various mandatory vaccines in India, but I recall taking the yellow fever vaccine when I was 32 and I had five days of fever

Similarly, I had a fever + 4 days of 20 hours of sleep after receiving the second Pfizer-Biontech dose.