If I get hair loss as a side effect of taking Lithium, will my hair grow back if I stop taking it? I won't stop it without pdoc's permission of course

See a dermatologist. First you need to make an attempt to define the condition. Hair loss is not likely because of Lithium. There is probably another cause. How much hair loss? Where? How long? The longer you take Lithium the more likely you will have low thyroid which may result in hair loss but is easy to treat. You can begin to understand the condition only after you see an expert.