I'm in a similar boat after hitting my 3,000 sub milestone. Like I was super happy about it, it was a big goal of mines, and it felt surreal, but indeed I've been a complete procrastinating mess right after it happened. On the bright side it's barely been a week since my last upload, so it's not like I've been out of commission for long..yet.
I find myself panicking more about what to upload next, and making sure it's of a high standard. I have all these crazy, probably unrealistic, fears too that are currently paralyzing me.
I keep trying to remind myself that every time I'm on the threshold of a big positive change, there's ton of fear trying to turn me around-and that I've regretted giving into the fear every single time. I need to find some way to push through my heart racing, and the "you're gonna muck this up" voices on loop in my head to just keep doing what I was doing.
Closest I've gotten is practicing mindfulness and literally doing all my ideas at once and seeing which one I latch onto/seems the most realistic to finish against a certain deadline.