If a PC becomes stunned on their turn, do they lose the rest of their actions without losing any stunned value?

Page 622 of the Core Rulebook defines the Stunned condition:

You’ve become senseless. You can’t act while stunned. Stunned usually includes a value, possibly over multiple turns, from being stunned. Each time you regain actions (such as at the start of your turn), reduce the number you regain by your stunned value, then reduce your stunned value by the number of actions you lost. …

I’ve created a creature that can stun a PC as a result of the PC attacking it with a melee weapon. This means that the PC could be stunned mid-turn.

Now, rules as written, the above paragraph reads like this:

  1. You can’t act when stunned.
  2. Stunned value "ticks down" each time you regain actions.
  3. Therefore, if you are stunned during your turn, "you can’t act," so you simply lose your remaining actions. Then, at the start of your turn when you regain actions, Stunned ticks down and you may be able to act again on that turn if Stunned reduced to zero.

So, if a PC takes their first action and become Stunned 1, they will actually lose a total of three actions: the remaining two actions on their current turn, then one action when they regain actions next turn.

Is this the correct interpretation? Or should Stunned start ticking down immediately, so that in the above example, the PC would lose their second action on that turn, go down to Stunned 0, and then be able to take their third action?