It isn't in your nature to get too stressed (Jupiter helps keep you happy), but if you've been feeling on edge lately, it may not be your fault. Research suggests that you can pick up other people's anxiety!
Some think it happens when you smell alarm pheromones in the sweat caused by a stressful situation. Just smelling the chemicals triggers the fear center in your brain even when there's nothing to be afraid of!
Blame evolution for your ability to perceive potential threats (even imaginary ones). If you don't want to be on high alert all the time, learn a few relaxing, meditative techniques. If you're calm, you can help your stressed-out friend!