Riding alone is simply a common wonder for me; as I easily become more afraid of the experience, however it's hardly different to riding with friends.
On topic, I have to lone-ride plenty of times wherever I go. Mainly because I travel to parks with a weary father, so I end up putting myself on the insane ones alone. If I have already rode a coaster or a certain ride with people before, it doesn't affect my experience at all if I was alone on that after; and most coasters don't actually bother me riding alone, if I've been on it or not. Drop Towers or similar rides of this kind can mess me about whilst alone, but I've already experienced two towers single-rided.
Notably, the first ride I had on Hurakan Condor, I had to ride alone because of the others chickening out, that I couldn't blame them, but whats the point in fear if you don't overcome it. But I'll leave a tip or two if you are in the same position as I was.
I managed to make an aquaintance whilst queueing which did ease my horrid tension and tempted mentality of simply walking off, this helps a lot if you are riding alone, as communication is the perfect remedy for fear when you are in a queue. Try to talk positively and make humourous conversation too, and as obsurd as it sounds, talk about how scary the ride is going to be with that other person, so you know you are both in the same position as each other.
Riding alone isn't bad, but it's not as enjoyable as riding with others, but it's dependant on yourself, if you're a social go'er or not, and single riding may differ to that person.