Getting into software development is similar. At first you get excited by your first "hello world", then you find all sorts of cool things that can be done with code. Eventually the passion flame wanes, you discover maintenance, management. The boring stuff.
First, realize that pretty much everything you get into will follow this pattern because everything has good and bad sides. Then ask yourself: are the bad things in filmmaking/SF start-ups more tolerable than the bad things in your current situation? Are the good things in filmmaking/SF startu-ups more enjoyable/rewarding than the good things you currently enjoy?
As far as happiness goes, maximize the amount of time you spend thinking about the good parts of what you have. Write code for a hobby project, use your money to indulge every once in a while. Dream about things you want to do.
Or just take the leap and do them. Then, you'll just have different good things to focus on.