If you are going to fast make sure you drink plenty of water and it is advisable to check with your doctor first. If you have a pre-existing condition you could jeopardise your health and you also need to take the weather into consideration. You should not exert yourself when fasting - i.e., you should not fast whilst carrying on working - make sure you fast as intended - to re-awaken and cleanse. To do this you need quiet time.
Hope this helps.