Too Much of a Good Thing?
Sun Salutations are indeed very energizing. They can involve jumping, they contain a big backbend (Upward-Facing Dog), which stimulates the internal organs, and they increase the heart rate. Ideally, they should be practiced with the sunrise in order to generate the liveliness and energy that we need at the beginning of the day.
Realistically, however, many people don't find it feasible to practice in the early morning. In fact, many prefer to practice in the evening, when they feel a bit looser or want a way to mentally ease out of the workday and into a quieter and more meditative state. If you tend to practice in the evening, I suggest that you make sure that the energy and heat of the Sun Salutation is balanced by poses and sequences that are more cooling and quieting.
Seated postures that involve bending forward, such as Paschimottanasana (Seated Forward Bend) or Baddha Konasana (Bound Angle Pose), and finishing postures, such as Salamba Sarvangasana (Shoulderstand) and Halasana (Plow Pose), are important for calming your system. They should balance the effects of the Sun Salutations, helping you settle down at the end of your practice so that your sleep isn't compromised.
Finally, make sure that you take a proper Savasana (Corpse Pose) at the end of your practice. Many yogis consider Savasana to be the most important of all the postures, as it is during these moments of stillness and relaxation that the benefits of yoga can truly sink in, so that we complete our practice in state of equilibrium.