You can pump up the passion again the same way you would when you are trying to rekindle romance or add spice back into a relationship that's gone dull-Remember all the reasons you fell in love with it in the first place! How did it make you feel when you first discovered this passion? Don't you remember the excitement the very first time you were doing what you loved? How your adrenaline was pumping, heart pacing, up all night can't sleep or eat, because the thought of missing out on something so spectacular kept was not a option?
Remember the reason why you loved your passion. What made you decide or choose this passion? If you didn't choose it and it's just something that manifested on it's own, how have you refined your craft? How can you make it better? I also think maybe the passion disappeared because you may not be inspired enough. Do something that will get you inspired again. Try something new. If life is interfering, then take some time out and dedicate it to your passion. Set out time. Make it fun. You should be back into the full swing of things in no time!