It's difficult to know what a person with mental health issues is going through if you haven't experienced such condition yourself. Sure, you could read Wikipedia; or, you can look at these illustrations instead.
Toby Allen is a freelance artist from the United Kingdom, and made this Real Monsters series to raise awareness about these conditions; from depression and anxiety to schizophrenia and post-traumatic stress disorder. Toby, who himself suffers from anxiety, has emphasized that his artwork is "not at all intended to make light of these conditions but instead is intended to give these intangible mental illnesses some substance and make them appear more manageable as physical entities."
You can learn more about Toby and his work here.