Things do slow down but not until you reach XP of 50
I would go into Options on the HUD and check what "Metabolic rate" is set to in case that got changed somehow.

Metabolic rate
Sets the rate at which your avatar needs to do things like eat and drink. You can select between High (fastest), medium and low.
When you start out you will get 1 XP from being active approximately:
High ~ 4.5 hours
Medium ~ 7.5 hours
Low ~ 12 hours

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