Technically as a medical condition insomnia has to be a significant period of time. Though there is such thing as transient insomnia...

Anyway, I have rarely had insomnia. There are nights where I have been stressed out, but the next morning I am exhausted so I tend to get sleep that day / night.

I remember the character Joel from our board. He tends to get chronic insomnia.

Try working out incessantly, doing exhausting activities (whatever they may be), and relaxing activities like hot baths. Don't do anything around your room that isn't sleep related, so you keep the association that bedroom = sleep room.

Anything else is probably largely psychological and I have no justification making suggestions about that.