I used to have tachy when I rolled over in bed, stood up, things like that set it off so many times a day. But you said it takes about 10 minutes to slow down. Is it gradual or just stays tachy for 10 minutes and pops back to NSR? There's a difference between the 2.
As for purple feet, white and cold fingers: sounds like Raynauds. That's more of a random vasospasm of the extremities. It can be triggered by stress, position or cold (even a bit of cold like walking through the refrigerator section at the grocery store.) I have this but mine isn't too bad, just embarrassing when my hands or just fingers change color. I can't sit without elevating my feet or within minutes they look dead. Calcium channel blockers work well for this. All depends on how severe you have it and whether its primary or secondary. I have primary (that's just Raynauds). Secondary means a person may also have an auto immune problem going on like lupus, RA, Sjogrens, etc. A rheumatologist can check for those.
There is nothing gradual about the return to normal rhythm. It rapidly increases, and rapidly decreases, which is why the Paramedics can never catch it in time. Once I was driving and it happened. I pulled over, called 911 and by the time they got to me, it had returned to normal.
Perhaps the doctor will recommend that you wear an event monitor for a month so you can record the events when they happen. That's the best way to catch them when the tachy seems to resolve so quickly, too quickly to see it at the office or to wait for the ambulance.