If the conditions are right he will be just fine, he will be a little more skittish though yes. That also kinda depends on where hes located in your house and what kinda cover hes got to hide in. You also won't see the natural Behavior's as much because in the wild they live in groups.
But It won't hurt him to be alone, and as Discuss are Cichlids, its a rule to keep them as singles or groups of 5 or more. 2-3 fish tend to fight more then if you had 4 + and one alone won't fight with anyone lol. I would say your good unless you want to add more fish, then in that case add 3 more at least and add them asap so the established fish doesn't come to think of the whole tank as his own space. Best of Luck
Edit: O ya and one more thing, with Discuss the key to keeping them healthy is water quality, water quality and water quality. Also a healthy balanced Diet of High Quality Cichlid pellets, Blood Worms and Brine shrimp. Never feed him just one food all the time. Feed him Cichlid pellets every morning followed by either blood worms or brine shrimp at night. Switch off between the two every other day. 25% weekly water changes as well are a must along with good aeration for that 84 degree water you have him in. Stick in a few Bubblers if you don't already have them.
