OED: 1. Acute longing for familiar surroundings, esp. regarded as a medical condition; homesickness. Also in extended use.
2.a. Sentimental longing for or regretful memory of a period of the past, esp. one in an individual's own lifetime; (also) sentimental imagining or evocation of a period of the past.
Nostalgia often idealizes the past by selecting only its affirmative qualities, thereby stimulating the Romantic emotions of desire and loss simultaneously.