How typical is it for mental health professionals to have a personal history of mental illness?

Both terms are broad: Mental health professions vary widely on amount and type of training. Also, there are even wider differences in types and severity of mental illness. It's unlikely that highly trained professionals suffer severe disabling mental illness as licensing & other credentialing would weed them out. But, it's likely that some have had personal therapy since they know it's helpful & life's not always easy.