It does NOT mean indifference. It means:
1. To be submerged, turned-over, or covered up. Or, more commonly,
2. To be so over-taken with emotion or excitement that one feels "turned upside down" or completely engulfed.
It does NOT mean "neutral" or BETWEEN "underwhelmed" and "
overwhelmed". If anything, "whelmed" means to be
overwhelmed or just slightly less excited than "
overwhelmed".