You know when you were a kid and everything that was new and exciting got you super inspired to do new and exciting things? Games were awesome. Toys were awesome. Medieval themed cosplay in the forest was awesome.
Do you still get inspired, as an adult, the same way as you did as a kid? Do you jump out of bed in the morning to do something that you're truly excited about? Is there a hobby or other activity that you do that you could do all day; an activity that you could be up all night doing, without feeling the desire to go to bed?
For yours truly, it came as a shock to realize a couple of weeks back that I was, for the first time in years, surprisingly inspired. It almost felt like I'd been living a more or less half-dead life since I started studying in the university. Maybe even earlier! I felt I'd been suppressing some sort of creative side of myself for such a long time that when it woke up again, I felt inspired like a kid again.
I cannot be sure, but it strongly seems that whenever you get a revelation like this, you've done something right recently. You've woken up a part of your soul that hosts your creative joy. So analyze what you did differently, and adjust your life to that direction to keep the joy awake.
There is, of course, the option of putting the creative joy to sleep on purpose, if you do not wish to live a life of child-like inspiration. I get it - it sounds childish, by definition - but it's up to you to decide if having child-like joy for things is the same not being an adult. Personally, I think a crucial part of being a grown-up is the ability to choose for yourself, and that includes the choice of living with creativity, joy, and inspiration, in the way that makes you feel like a kid again.
My advice: embrace whatever makes you feel inspired. Live out the creative joy within. But more importantly, choose for yourself.