Conversations that people have when they are in bed together can be referred to as pillow talk, especially when they are about secret or private subjects.
pillow talk in British English
noun
intimate conversation in bed
pillow talk in American English
noun
private conversation, endearments, or confidences exchanged in bed or in intimate circumstances between spouses or lovers
Word origin
[1935–40]
Examples of 'pillow talk' in a sentence
pillow talk
We figured there was a lot of pillow talk about us.
Christianity Today (2000)
We were having a pillow talk about it one night and I said it would mean me earning more.