How to prevent work from exacerbating situational depression?
You are mistakenly conflating hours spent in the lab with productivity. There is certainly a point of "diminished returns," where extra hours don't actually improve your productivity, and actively harms it in the longer run.

A few ways to change up your routine:


Work on your most important task first thing in the morning.
Focus exclusively on your work for 20-30 minutes at a time. This means no checking email, no chatting with lab mates, or other distractions. After you're done with your block of time, take a few minutes to recharge before restarting (or moving to a new task).
Avoid obsessively checking your email. Pick a few times per day to answer your email and engage in social media, and stick to it. (And don't spend multiple hours during such sessions; figure out what's important and what isn't, so that you can be finished in 15-20 minutes or so.)


You'll find you probably get more done in less time following such an approach than just spending tons of hours in the laboratory. This will also give you time for your personal life, which brings me to my other point:


  "Block out" time in your schedule for "recharging" activities.


The nature of the "recharging" activity will depend on what works best for you: some people exercise, others engage in artistic or creative activities, and still others meditate. It doesn't really matter what you do to clear your mind and "recharge your batteries"; however, you should make time for it, and make sure that you stick to it. It doesn't need to be an extensive commitment: even an hour or two per week can suffice.