IreneQ raises some probing questions about the dangers of fasting, praying, and having intense worship experiences. Yes, you read right. These things can lead to idolatry if we enter into them for the purpose of trying to use them to get something out of God, acting as if your prayers will be more effective if you fast or if your relationship with God will be more fulfilling simply because you've engaged in certain practices like certain worship experiences.
That doesn't undermine fasting, praying, worshiping God, or worshiping God and having an emotional experience, in a group of privately. It does require examining your motives. Are you doing this to get something out of it, even something in your relationship with God, or are you doing it to worship God or to honor God's revelation that he wants us to treat him as a Father who gives to his children what their sanctified hearts long for and ask him for? If it's the former, it seems an awful lot like those Jesus warned against who think that they'll be heard because they use many words. Use of intense emotional experiences isn't any different. Such attempts are strikingly reminiscent of the prophets of Baal on Mount Carmel who thought tearing their clothes, shouting loudly, and making all the right rituals would get the attention of their god. Do we want to treat God that way?