Oh the emotional crash after an event (or even a long workout) you've been training for is very common and very real. Some of it comes from the endorphine crash...you ride high for months while training or even hours after a hard or long workout....then crash hard. Some of it comes from building your life and schedule around an event and then when it's over...once the goal is attained, there is a huge void where the goal used to be along with the lack of endorphine rush. Knowing it's normal is helpful. Staying active after an event or not letting too much time go by before another workout, even if it's not a long one will help a lot too. There are lots of articles about it on Livestrong.com or Active.com such as this one that might help:
As for the weight gain...that is common too. Endurolytes pack sodium which you need for an endurance event or workout. But they allow you to retain water, which is great for a workout, not so great on the scale. Also if you are doing an event that requires a lot of muscle, like a long or hilly bike, you are creating a lot of lactic acid. They say you should not weigh yourself after lifting weights because your body is reacting to and recovering from the expansion you just required of your muscles. The same is true of an intense and or long bike or run.
Hope that helps.
“A person who wants something will find a way; a person who doesn’t will find an excuse.”