If something is constricted, it's squeezed or inhibited in some way. If your neck is constricted by turtleneck sweaters, you might feel more comfortable in a sweatshirt.
There are a couple of different ways to be constricted. When someone has a serious allergic reaction to shellfish or peanuts, their constricted throat, which is swelling and narrowing, requires immediate medical treatment. If you're constricted by your seat mates on an airplane, you simply feel like you don't have enough room to move around freely. You can also be constricted more figuratively: "I feel so constricted by my curfew — I can't stay out past 8 p.m. on school nights."