If its actually Achilles Tendonitis, stop training. Start rehab.
Dont make it worse. It takes time to fix.
Do not rush it or you'll be a mess
It is not. It is the best description. I know what you mean.
I wanted to just put Achilles, but that apparently isn't an option... I'm not sure if I would even personally call it the Achilles, it's that spot, but I amn't sure that it's actually the tendon. Let's hope not.
Is Achilles sore to touch? Does it hurt when you get out of bed in the morning?
If it does get bad it is a very very hard problem to fix, months not weeks. Make sure to stretch your calves and hamstrings as often as you can, an issue with them can manifest itself further down the leg.
No harm in spending a few Krone on a physio just to be safe. They can check to make sure the legs are ok, not just the achilles.
Horror story.... Paul Nolan's Achilles has seperated from his heal due to excessive training through injury/ train extremely hard on hills....