How do you get 'overheal' in Deus Ex?
Solution 1:
If you've got exactly 125 health, it seems very likely to me that you inadvertently popped some Painkillers - they give you 25 health, if you're already at 100, or up to 50 if you're below 100.
Besides Painkillers and the Hypostim, certain types of alcohol (beer, wine, vodka, and certain mixed drinks you can order in bars) can also increase your health above 100, but it tends to be in increments of 10 health, which seems like it would make reaching exactly 125 difficult.