Good thinking for checking to see if he is clingy because he is not feeling well. That was my first thought. If he's fine otherwise, maybe you could sit on the floor and put your legs in a V position and set him in the middle between your legs with some toys on the floor in front of him. This way, he would still be leaning up against you but sitting on the floor also. Or, sit/lay him on the floor in front of you and hold his hands while playing pat-a-cake, or other songs. Or lay him down and hover over him while being silly and making him laugh. Basically, any way you can put him on the floor while letting him know you are right there with him should help him be more comfortable again. You could do this for small amounts of time and gradually increase the time as he gets used to it.
Maybe if he has been around a lot of new people and strangers lately, he may be just wanting some one-on-one mom and dad time. Or, maybe he's trying to adjust back into his old routine after maybe being a little off schedule for a couple of days.
I think babies need to be held a lot anyway and there's no harm in holding a baby. But, they also need floor time in order to develop muscles and to learn that they are safe even when not being held. I think it's best to find a good balance. Sounds like you're doing a good job of that!