Mental health
Everyone has mental health as well as physical health and thinking about it going wrong can be just as scary, perhaps more so, because it is often less obvious than a cold or a broken arm.
You might notice any or all of these signs:

becoming moody
having trouble sleeping
feeling unusually anxious or on edge
feeling down
having gloomy thoughts a lot
losing your mojo
snapping at people
not feeling like yourself
losing interest in friends
cutting yourself off
wanting to hurt yourself
wondering why other people bother with you
hating the way you look
feeling everyone hates you
feeling trapped
depending on food, drink or drugs to feel better
Some of these things happen to everyone at some time. For instance, if you lose your job, or no-one seems to understand you. Maybe you are stressed by a move, or exams, or a new baby. Perhaps someone close to you has died, or let you down.
How well you cope depends on your emotional resilience and sometimes that needs some professional help. Rather like how well you recover from a bad chest infection depends on your immune system, but can be helped by antibiotics. Counselling is here to help you put the pieces back together and feel yourself again.