Pension fund keeps growing - thoughts?

[Brave Fart]

My pension is a bog standard Aviva defined contribution scheme, and over the last year I have fallen in to a routine of checking the fund value regularly on line. I do not manage the funds in any way - I leave that to the fund managers at Aviva!
I don't mind equity risk since I also have cash savings and own two properties. I have zero debt.
Thing is, it just keeps going up - about 20% in the last year. The fund is invested 80% in global equity, only 4% UK equity, then bonds and cash; I semi-retired recently and no longer contribute since I'm in my mid fifties.
I have a few questions for the wise owls of PH:

• Am I making the mistake of short-termism, and am simply seeing a short term bubble?
• Why does the fund keep growing - is it because of the global economy?
• Any opinions on how long this can continue (I know no-one has a crystal ball)?
• Is there any way of "locking in" these recent gains?
• Should I just leave it alone, since I'm not drawing down yet (and won't for a few years yet)?

Please don't think I'm bragging here - I'm simply curious because it seems too good to be true, and wondered what others' thoughts were.