Nearsighted + lattice degeneration + RD in one eye + Valsalva maneuver = significant risk of RD in the fellow eye. Note that, of these risk factors, there's only one over which you have control, that being whether you choose to Valsalva. So for now, I suggest you avoid it.
As for your lifting career going forward, if you are dead-set on lifting heavy again: Explain to your doc how important this is to your quality of life, and ask whether prophylactic treatment of your lattice would reduce your RD risk. (I have to stress that I am NOT recommending this, because even with prophylaxis you will still have a higher-than-average risk of RD. That is, there is nothing your doc can do that will reduce your risk to the population baseline.)
Unfortunately, I suspect your doc will say you're not a candidate for prophylaxis (lattice is often not amenable to prophylaxis, especially in the context of nearsightedness). As you observed above, sometimes life sucks.