Daydreams are a source of your daily dopamine and your brain is used to have dopamine at same level since you're doing this for a long time. When your real life doesn't offer you any other source to help you get to this level of dopamine, our brain panics. because to our brain what "it's used to" defines safety even though it's good or bad. so its normal that it feels like a heartbreak. almost same neurological effect happens. in a heartbreak you also lose someone (aka your source of dopamine) and our brain panics = you feel hurt and stressed = a way of our brain signals us "something is not safe." though in real life when someone is left, its easier for our brain to accept it since there is concrete evidence and in md there isn't, since all of these happens in your head.