Implantation Bleeding VS Period

Hi all,

I was shocked last night to start my period four days before it was due. It started fairly heavy- brownish. Then slowed down in the night and has been very slow today, only needed to change my tampon once. I am normally a very heavy bleeder and in the first few days need to change every hour or so. Also, I've had no cramping and no pms symptoms, even my husband commented that I wasn't as moody as usual. I am now starting to wonder if it's heavy IB? Or is that just wishful thinking? If anyone has experienced heavy IB can you share your experience?