Psychic attacks are probably the most dangerous kind of attack as they can't be disproved or proven very easily. In fact, it's hard to convince some that they exist at all. However, they do, and the signs and effects tend to be very distinct.
There are many types of psychic attacks, from the general attacks on your psyche by advertising agencies to the more dangerous direct attack by people or worse.
It is said that 90% of attacks are unintentional, brought on by our picking up on people distress, needs or emotional baggage. If you're especially empathic, then a relative or partner having a distressing day can make you feel just as bad, or feel overwhelmed with emotions that aren't actually yours. It's very possible that people who are often depressed for no good reason are picking up on the negativity from others around them. The other 10%, though I personally suspect that this figure might be higher(!) are actually deliberate attacks by another person or an entity. Having seem both things, I can say neither are much fun.