WHEN IS THE BEST TIME TO PRAY FOR HEALTH?
Question What is the best way to daven for a person’s health? Answer In Shabbos (32a), the Gemara says, “L’olam y’vakeish adam rachamim shelo yecheleh, a person should always seek mercy from Heaven that he not become sick.” When is the opportune time to ask Hashem for this? “L’olam, always.” A man should always turn to Hashem whenever he has the chance. As you walk home tonight, when you’re lying in bed, when you drive around the corner, as often as you can think about it — pray to Hashem not to become sick. And, the Gemara adds, “Because if he becomes sick, then ordinary prayer will not help.” The Gemara gives an example. Suppose a man walks out on the street in Rome and a husky Roman soldier puts his hand on his shoulder and says, “Come with me.” For a few coins, he can get out of it; a small bribe will free him. However, once he is brought to the court it’s a different story. Then, he needs a great deal of money to be freed. When you fall into bed at night, it should be to you as if you ascended the court tribunal in a Roman court. Roman judges didn’t take just a few pennies. You had to have a big bundle of money and know how to hand it to them. You couldn’t hand it personally to them. You had to have go-betweens who knew how to hand it to them. Therefore, the best time to pray for good health is when you have it.When a man is already, chalilah, ill, then he needs teshuvah umaasim tovim. He needs big-time lawyers. Teshuvah umaasim tovim are not easy. Therefore, a man is expected at all times to worry about himself in this way, praying to Hashem. The Gemara says further that even tefillah — praying with kavanah — is included in gemilas chasadim, in doing kindness. That is a strange thing: Praying fervently is included in doing kindness? However, Rashi explains that this is because it’s a kindness to yourself. You’re doing yourself the biggest favor if you constantly pray to Hashem to keep well. And that is part of our hishtadlus, the normal efforts that are expected of us.

Miller, Rabbi Avigdor. Rav Avigdor Miller on Emunah and Bitachon . The Judaica Press, Inc.. Kindle Edition.