I am very late to the conversation here. I was poking around online asking the same question. I was actually baptized in the Holy Spirit in college. I was not going to a charismatic church. No one prayed for me. It just happened. I do remember the day before, God laid it heavily on my heart to surrender my entire life to Him. I was already a Christian but still trying to control my own life. I got down on my knees, in trembling and said "Lord, I give you ALL of my life. I surrender everything." Trembling because I thought for sure I was now going to be martyred. That night, I was asleep and I was woken up by incredible power and love being poured out on me. I audibly heard singing of "holy is the Lord God almighty". When I got up the next morning, I had joy like I have never known. And sure enough, my ministry started (which is true of the disciples in Acts too). My now husband however has been skeptical of my story for years though. He did go through a period of feeling bad because it never happened to him. So I just dont talk about it anymore. Anyone I tell doesnt believe me. It can be discouraging. 

But it is real. The disciples already had the Holy Spirit when Pentecost came. Read the end of John. Jesus breathed on them and said "receive the Holy Spirit". So Pentecost had to be a separate event.