I would check into the laws surrounding Mental Illness protection in your state. If you aren't in a high risk job I don't think they can fire you but I am not sure, and if they really want to fire you they will find a way unfortunately.
Getting help though can be life changing. What would your life look like if you didn't have to battle the paranoia and delusions? What could you do that you aren't doing now because of them? You must be so tired. Battling it on your own can be so difficult. And they will give you a label although it may not be right away. Sometimes they wait a couple of sessions to see how things are going first.
In the meantime if you are bipolar taking omega oils - I take 4 pills a day. helps a bit according to some research I've seen. Helps a bit. Not a lot but I notice a difference. At least it won't hurt you and isn't terribly expensive.
If your lose your job because of a mental illness label then take them to court, as that's not right nor fair. I agree there are poeple out there with stigma so maybe seek treatment and make it clear that you don't want a label or diagnosis and just want to be treated for what they think it is. They may be open to that if you explain why or they may not, but at least you tried. I think if this is impacting on your life then i do think its important to get help, and if it is schizophrenia or bipolar i don't think you can do that alone. Maybe get your partner to go with you to appointment that might help.
Freddie
If you have a mental illness, learning the "label" for it doesn't change what is happening. If you are having as much trouble as you describe then it is time for medical intervention. Yes, they will give you a diagnosis but you can't get treatment unless they have a way to characterize your symptoms so they will know what medications to prescribe. Go in knowing there will be a diagnosis, and that it doesn't change who you are, and you can get help.