I have late 20s friends and have seen the similar behaviour. A lot of people I meet say they are in a bad place mentally. Also, pardon my ignorance, but I am a

I have late 20s friends and have seen the similar behaviour. A lot of people I meet say they are in a bad place mentally. Also, pardon my ignorance, but I am also curious what counts as being diagnosed with "anxiety" disorder? As in are there definitive definitions of these things?