Erotomania, also known as de Clerambault's Syndrome, is a mental disorder where the sufferer believes another person is in love with them and cannot be shaken out of this belief. The other person may be someone who is a celebrity, someone who is wealthy, an ordinary acquaintance, or even someone who is a fictional character or completely imaginary. It is an extreme form of the unrequieted love experienced by many people and which can lead to the socially disruptive activity commonly known as stalking. The Wikipedia article has a far fuller and more clinically detailed description of the condition, and it is worth noting here that the condition is associated in its extreme form to both schizophrenia and bipolar disorder. Some psychologists working in the field have noted that if the sufferer can be brought out of the delusion that the loved one will come to them, and realise that the love is completely one sided, the consequent sense of loss and emptiness can provoke a deep depressive state.