How do I build a client base when I'm terrified of the income?

You want to help people get healthy. You have no clients yet, or too few, and the money is not steady. That gap between what you can offer and what you are paid feels like proof you are not ready. It is not proof of anything except that you have not started enough times. Notice what you are actually afraid of. Not the work — you already know the work. You fear the empty calendar. You fear the silence after you ask someone to work with you. You fear that nobody wants what you offer. That fear is not wrong. It is just not useful to you right now. Here is what is within your control: who you talk to today, what you offer them, and whether you ask clearly. The unstable income is a fact about your current actions, not a verdict on your future. Change the actions, and the income changes with it. If the fear sits heavier than this — if it keeps you from sleeping or eating — talk to someone you trust, or a professional. That is not weakness. That is sense.