Mine did the same in late winter indoors. In Texas it is in the 80s now in daytime. I tossed mine outside and in only 3 weeks it has exploded with new leaves. They love sunshine and warm weather.
Yours might just be doing it's winter dormancy thing. I read once these trees from China are actually act like deciduous in the go dormant in winter. Though they can't handle below around 40 degree low night time temps.
Leaves are good to watch for trouble but the flowers are too. If it is still pushing flowers you are ok.
My personal Gauge with mine is:
No flowers no buds - unhappy plant.
Buds but not blooming - deciding to be happy or not.
Buds blooming - tree is doing ok
New leaves and buds blooming - growing happy tree
PA is not ideal for tropicals but with a sun room you might be able to pull it off.
Good luck!