Sick with love
The Rambam (Maimonides, Mishnah Torah, "Laws of Repentance", 10,3) writes: "What is the proper love that we must have for G-d? It is to love G-d with an exceedingly great and intensely powerful love until the individual is constantly enraptured by it; he must be stricken like a lovesick person, whose mind is at no time free from his passion for a particular woman, with the thought of her filling his heart at all times, whether he be sitting down or rising up, whether he be eating or drinking. Even more intense should the love of G-d be in the hearts of those who love Him, and this love should constantly absorb him, as we are commanded to love the Lord "with all your heart and with all your soul." Solomon expressed this allegorically in the verse, "for I am sick with love." (Song of Songs, 2:5) Indeed, the entire Song of Songs is an allegorical description of this love".