form of list

[Ashiuhto]

Is the form of the following list correct?

Definition of insomnia：
１. Hard to fall asleep
２. Easy to wake up
３. Wake up too early

[Gillnetter]

Is the form of the following list correct?

Definition of insomnia：
１. Hard to fall asleep
２. Easy to wake up
３. Wake up too early

It is not the form of the list that you are asking about. You are asking about the various items in the list. All of the items in the list are acceptable.

[Ashiuhto]

Which is acceptable, 'Definitions of insomnia' or 'Definition of insomnia'?

[Gillnetter]

Both could be correct. It depends on the context. If you only have one definition, us definition. For more than one, use definitions. A definition of a man is male. Some definitions of a man are: a male, a primate, and a biped.