I think check with someone. Being in over your head means that you feel like you've blown things out of proportion or you're speculating but aren't sure about something. Asking someone else for their opinion and advice is really helpful.
All of those ARE reasons why communicable diseases kill fewer people today except for B. Your answer is B.
Prolong feeling of sadness, loss of interests, angry outbursts, tiredness, sleep disturbances, anxiety, loss of appetite, slowed thinking, feeling of worthlessness, frequent/reoccurring of suicidal thoughts, unexplained physical problems and having a hard time thinking. [These are just a few symptoms]