Thank you so much for your explanation and patience. Now I understand them all.
Originally Posted by Hi_there_Carl
The sentence "I am getting a good idea." could be restated "I am acquiring a good idea." 'To get' in the case you describe means 'to acquire'
To fall in love is to begin to experience feelings of love towards; "She fell in love with her teacher"
The word fall is used to to convey the idea of passing suddenly and passively into a state of body or mind
Here are some examples of using the word fall in this way:
"fall into a trap"; "She fell ill"; "They fell out of favor"; "Fall in love"; "fall asleep"; "fall prey to an imposter"; "fall into a strange way of thinking"; "she fell to pieces after she lost her work"