Hi there montreal home grown. Sorry for the late reply I know you are working today already. I hope it's going well. I have worked and trained through a 30 day fast so I know it can be done. I was healthy then to begin with but had no trouble lifting, exercising and riding a motorbike the whole way through it. It depends on how much toxic crap your body has to cope with while fasting, and how urgently it decides to do it. The best advice I can offer you is to make plans to deal with weakness or other crises, but don't actually anticipate them. In other words, work out ahead of time how many days off you can take from work- if needs be. Or how you can correctly and safely break a fast at short notice if you can't take time off work but the fast becomes too difficult under that workload.
If you are healthy enough to start with you may actually find that fasting gives you more energy and strength at work! A lot depends on that.