Stop looking down!
I was recently driving cross country in a U-Haul (without AC-not recommended!) and I noticed that my eyes and neck were getting super tired. Why? Because I was only looking forward and down, not using my peripheral vision, and staying static in my upper body. (I was also tense because it was a 14 foot truck, but I digress). So where are your eyes right now, and where is your head? Pointing down at a smartphone? Looking down at a book on a plane/train? Walking and texting, with your spine slumped? Or looking down at a music stand?
Simply put, where your eyes go, your body follows. Try this:
Turn your head to the left while looking to the right. Reverse.
Look down while tilting your head upwards. Look up while bringing chin to chest.
Look down at your cell phone.
Your first instinct is to flex your spine and bring your head down, right?
So first thing, start giving your eyes a break. Don't just look forward, look up, look sideways, make circles with your eyes, etc. Notice how your head, neck, and spine position changes.
Second, take a look at your music stand. I recently played a duo with a vertical advantaged friend of mine (he's 7" taller than me, and I'm 5'7"), and it was incredibly hard for him to play with me without major spine slumping. Why? Because my stand was so much lower than his, he felt like he needed to bring his down, and then bring himself to my diminutive height. So here's the thing- the stand can be any height (within reason) but you have to make it possible so that you can stand or sit comfortably and not move your whole body. If you, for example, sit near someone in orchestra who's much shorter or taller, you may have to compromise. Challenge yourself to keep integrity in your spine and look up or down with just your eyes.
Third, stop looking down to text. Bring your phone up to your eye level for a change. And please don't text and walk. You will either trip (or be hit by a crappy driver) or be plagued with awkward neck pain.
And remember, where your eyes go, your head follows. So if you walk/run/lunge/yoga with your gaze down, your head is probably following along for the ride (and your spine).