It's not the end of the world!
If you are a BOOST LITE user, you'll have your speed reduced or "throttled". Meaning basic email and webpages will still load, but rich media formats - video, music, etc - will be significantly impacted. Don't worry though, this applies to overseas connections only - domestic speeds will not be affected. Purchase a data pack to restore speeds. Notice that you keep exceeding your 100GB? Let's talk about upgrading.
BOOST UNLIMITED users who go beyond "fair usage" data consumption will also have their speeds reduced or throttled until their monthly renewal date occurs. Please contact support for more details beyond fair usage limits.