The pain I felt was from a Dropped Metatarsal. I can't remember if this is an official diagnosis but that's what I call it.
The metatarsal is the bone that connects the toe to the arch of the foot. The cuneiforms and the cuboid (of 'Born to Run' fame) are the row of bones comprising the arch where the metatarsals attach. The illustration below is provided by none other than Leonardo DaVinci, who, when he wasn't too busy painting the Mona Lisa or inventing flying machines, studied the human foot and called it, "A masterpiece of engineering and a work of art."
The individual bones of the foot are connected by joints. Just like any other joint, they are succeptible to becoming restricted, inflamed, and tender. The second and third cuneiforms, because they comprise the apex of the arch of the foot, are especially prone to becoming fixated. When this happens, pain can develop on the underside of the foot, often right in the middle where the cuneiform abuts the metatarsal. It is especially pronounced when going barefoot on hard surfaces (which I can attest to.) It can also affect the ball of the foot where the metatarsal attached to the toe, which often creates a pain similar to stepping on something sharp.
Typically a fixated metatarsal is stuck in a pushed down position, requiring me to literally push it back up to free up the joint. This is why I call it a "dropped" metatarsal.
The best remedy for this issue is to have the foot manipulated to restore motion to the affected joints. In simple cases the pain will often immediately improve. I recently treated a severe case of this that required 5-6 visits on my part to finally get the stuck joints released. However even in that case the pain improved immediately once we succeeded.
This is a condition that I find frequently accompanies other foot issues such as plantar fascitis or neuromas. It is not uncommon to have a runner who has been diagnosed with these other conditions, when in fact the most tender spot on their foot is the restricted cuneiform/ metatarsal. In some of these cases once we free up the joint issue the remaining plantar fascia or neuroma pain turns out to be less than what was thought, if at all. The severe case I mentioned above had been diagnosed with both of these conditions, and, having had no luck with conventional treatments was facing surgery.
Ultimately the key to preventing this from happening again is to better support the arch. This is done by either increasing the amount of arch support with shoes and/ or orthotics, or by strengthening the muscles that provide internal support. If you've seen me or read any of my other posts you can probably guess which approach I favor.