Hi DND,
The above members are correct that it is over watering. I have the same Hoya cultivar that you have and it is dormant during winter. Mine is growing in an East window. They don't like full sun, especially summer. I keep mine on the dry side during winter. When new growth or faster growth, then I water more but allowing top soil to dry first. Mine sometimes bloom in the Fall, but it is a Summer blooming plant. The scent is heavenly. BTW they like an acid soil.
It is not a hard plant to grow if you understand their needs. I used to have more cultivars when I lived in a house with large windows. The name is H. carnosa variegata.
Trim your plant back hard---to healthy leaves to lessen stress on the plant while it recovers. Also remove any dead leaves.
