Our established bougainvillae experienced a very sudden change. In one week, it went from lush and healthy (R) to sick and maybe even dying (L). We live in Zone 9, and had a 3-day heat wave over 100 degrees. The thing is, it's 5 years old and has experienced hotter weather for even longer period of time in the past. We just don't know what suddenly happened. We soaked it well and now are praying for a good recovery. Has anyone else had this happen? No bugs that we can see.

How much fertilizer and what kind did you use?

The flowers are very thin. Normally a boogie doesn't not bloom in intense heat.
If you had unexpected high temperatures combined with thin, flimsy flowers, this could be nothing more then heat stress causing bloom drop.