Depression manifests itself differently in everyone. It ranges from being completely unnoticeable to wanting to die because you are in so much pain.
How bad does it have to be before you can convince yourself you need/deserve help? Hopefully it doesn’t have to be bad at all. I’m going to share a secret with you. You deserve help no matter what you are feeling. There is no minimum requirement for getting help. The question is: do you want it? Only you know what you need. And whether you need it or not, it’s OK to want it.
The other question you might want to ask yourself, is why you have to convince yourself that you need or deserve it, before simply going out and getting it.
Feeling undeserving of help is a very painful place to be, but that’s a perfect place to start therapy. The fact that you question whether you are deserving of help, is reason enough to be in therapy. I wish you all the best on your journey.