This hangover effect does exist for pastors. Have you ever noticed that many pastors take Mondays off? There's a reason. Preaching a sermon is hard work. Leading a church service including preaching the sermon, teaching a Bible class full of people of very different backgrounds, interests, and abilities to engage, then in many cases leading another service like the first one and later in the day a service which is different from the first one - that's several days' worth of work. I've read somewhere, but don't recall where, that preaching a sermon or teaching a class is, for most people, the equivalent of about a half day's work. Speaking from experience, on the occasions where extra duty has called and I've found myself leading no less than four church services and a Bible class, let's just say the rest of the day is rather vague.
Why would people go through all this? It's plain and simple. Christians confess that the Easter celebration is a time to remember that Jesus, the Son of God who gave his life for us, rose again from the dead, showing that he had conquered death. This is great news! It's worth a little extra effort to remember it. It's actually worth all that we can give it!
Where does this "post-Easter hangover" come in? Well, I confess, I'm going to be a hard-liner here. Easter is a season. It is a time period of 49 days in which we spend special time remembering the life that we have in the risen Lord. He visited his disciples in different ways. He appeared to many people in large groups. He gave his followers various special instructions. After 40 days he was taken from them and ascended into heaven, from where he sent the Holy Spirit in a great outpouring on the 49th day, in Jerusalem (Compare John 20-21, 1 Corinthians 15, Luke 24, Acts 1-2).
I might get around to that post-Easter hangover. If I do, it'll be on or about May 25. Easter is a season. Welcome to Easter!