is a good habit and is quite safe if done properly with all aseptic precaution. The kind of complain you are mentioning suggest that you might be having a fall in blood pressure which could b due to plenty of reasons. The best way would be to take rest with legs elevated, take plenty of fluids and juices. Keep measuring the temperatures. 97.4 is OK and you shouldnt be worried about it. If in case you have a fever
which can happen if aseptic precautions were not followed during putting a needle then you will have a fever with a raise in temperature. In case such a thing develops, do visit a physician who would like to do some blood tests. Untill then take rest and dont worry much. You should be fine by tomorrow,
Hope I am able to solve your concerns.