You can modify by keeping your head on the floor but keeping your abs engaged or put a pillow under your neck and shoulders for support but don't forget to engage your abs at all times.
I've done pilates for about 4 years off and on. Trust me, I started out with head on the floor then moved to pillow, and eventually being strong enough to not need support.
Also, make sure your you're keeping your head in a neutral position. Imagine that you're holding an orange under chin so that you're not looking down, that helped me A LOT!
Keep at it :-)
| Pounds lost: 17.0