One of my English professors gave us some very helpful information when giving us writing assignments:
1) There are very few stories/events/experiences that are "new"in this world.
2) But OUR experiences are "new" to us - and that's what we are to write about.
Examples: Giving birth, grandchildren, breaking a bone, losing a friend, having a car accident.
There still are firsts "available" - such as landing on Mars, etc. - but most of us won't be doing them.
By the way - to the original poster - are you also dealing with depression or bi-polarism? That could also contribute to the crashing from happy to not happy.