The Captain said he was focused on the flap setting and was looking at our EICAS waiting for a flap malfunction to appear and was unaware of our pitch attitude until I queried him. The Captain said he did pitch forward, but didn’t think he pitched forward enough to cause such a dramatic pitch change and concluded we must have hit windshear or a downdraft. Neither of us heard or witnessed the Predictive or Reactive windshear warnings but we did hear the GPWS cautions and warnings