Anxiety and depression
The danger of isolating yourself is that you cannot practice how social contexts work. It can cause you to isolate yourself even more. If you have high absence from school and rarely meet friends, you may feel sad and depressed.
Good advice
There are many good tips regarding anxiety and depression. Among other things, what effect exercise, food and sleep may have for your wellbeing. Good information about this is available on the page Youmo.
Link to Youmo English - feeling bad
Link to Youmo English - tips to feeling better