Can't sleep? The Pennsylvania Ballet premiered a most delightful ode to insomnia in Matthew Neenan's Somnolence on opening night Thursday at the Academy of Music for the company's season finale program, Re/Action.

But first, there was disappointment: Principal dancer Amy Aldridge, who will retire Sunday, would not be performing, nor would we see Balanchine's pas de deux from Rubies, which Aldridge had been scheduled to dance with Alexander Peters. (Ballet spokeswoman Veronica Mikitka Reed later explained that Aldridge was suffering from an injury flare-up, but that she hoped to dance remaining performances.)

Further, this would be one less chance to see Peters, another popular principal dancer, who will leave to join the Miami City Ballet after this weekend's run, as will corps de ballet dancer Harrison Monaco.

Now for the good news: Set to Vivaldi against a backdrop that looked like a tufted mattress, and with a pyramid of pillows large enough for the dancers to climb, Somnolence is both ethereally beautiful and hilarious. The dancers slide on their bellies perched on pillows, have pillow fights, and use pillows as stepping-stones. They crowd-surf, kick restlessly, have romantic interludes, and frolic in their jammies.

Aldridge was supposed to have danced a pivotal role Thursday night, but she was replaced by Holly Lynn Fusco, a longtime corps de ballet member, who ably managed a pas de trois of pillow time with Ian Hussey and James Ihde.

The company's Balanchine heritage is represented by two pas de deux. Tarantella, fast and fun, was danced by Mayara Pineiro and Jermel Johnson (although notably a signature Aldridge role). Thursday night's most beautiful dancing was from Lillian Di Piazza and Hussey in Balanchine's Tchaikovsky Pas de Deux, highlighted by Di Piazza's fluid arms and deliberate timing.

The Pennsylvania Ballet also offered two previews of the 2017-18 program. Dayesi Torriente and Arian Molina Soca danced the Black Swan pas de deux from Swan Lake, a beautiful contrast of hard and soft emotions and movements. Maslova and Sterling Baca performed the pas de deux from Sleeping Beauty, which was delicate, deliberate, and deliciously sweet.

Pennsylvania Ballet. 2 and 8 p.m. Saturday, 2 p.m. Sunday. Academy of Music. 215-893-1999, paballet.org