in this sentence: When she was discontented, she fancied herself nervous.
What would be a more exact meaning of fancied:
1) she pretended she was nervous...
2) she imagined she was nervous...
For example, when Mrs Bennet ("Pride and Prejudice") had the slightest annoyance, she fancied herself nervous. It means she started to complain that her poor nerves were under so much stress and that nobody cared.