Owning your own business puts you at dire risk of imposter syndrome. You feel you don't deserve your success, that it's luck or timing and you've deceived everyone into thinking you're successful. There are those who will tell you as much, people who think it's easy and don't see the work. You've probably had a lot of help getting to where you are, but it wouldn't have been possible without your extreme level of effort.
This can mess with your mental health. You can be in a constant state of anxiety about the sales of the day, the customer reviews, the overall economy. This happens while your business is growing and you're becoming objectively successful. There is no "end" to this game of business and there is no rest from the tyranny of growth. It's sink or swim, they'll tell you. You're a shark that has to constantly swim or suffocate (not entirely true). Most of this pain is self inflicted.
There is also no net. If you have a job, you have unemployment, but not the small business owner. Employees get workers comp insurance. I've had such insurance for only two years of the last twelve. If your business fails, you are legally liable to pay your employees first, then your creditors, then your investor loans, and only then, do you get a piece of the pie you made, along with 100% of the tax burdens. You are on your own and only someone in your position will understand this.
I characterize small business as two steps forward, one step back. The steps back are infuriating and can get you down, especially when you can often blame other people in the industry and not outside forces. In the beginning, it's one step forward and two step back. Many who weren't prepared for this end up failing. In the middle, the most excruciating part, it's one step forward, one step back. At times I wished the business would just fail or succeed, either one. Just remove me from this life wasting purgatory. Eventually we started taking two steps forward. That took years.
The solution for me, despite being an introvert, is networking with my peers. This is a lonely trade and we're all silos in the wilderness. We reinvent wheels and deal with mostly the same problems and often alone. If you're feeling overwhelmed, ask for help. You are not an imposter. You are doing the thing. And if you are suffering, you deserve to be free from that.