Answer:

I agree with this idea. Although being with others is enjoyable when you're already in good spirits, it can be exhausting when you are stressed out. On the other hand, when you are by yourself, you are free to truly do nothing and let yourself unwind. You can also focus on your own particular little pleasures, rather than shared activities that might not reduce stress very much. Finally, when you're alone, you are given the quiet atmosphere necessary to organize your thoughts and plans.
When you are around others, especially friends, you feel an obligation to keep actively doing things. Rarely do people just sit in silence together! Maybe you go shopping with your friends a lot or go to the park down the street whenever people visit. Even if you're just sitting and talking with your friends, you are engaging with them. You're thinking, listening, reacting, speaking, telling stories. Normally, this is fine and enjoyable. But if you're extremely stressed out after a hard day at work or school, it can be burdensome. Interacting with someone takes energy. If you're already exhausted and frazzled, it doesn't help things.
Alone, you don't feel this requirement to be energetic and fun. You can take a nap. You can meditate. You can lay on your couch and count all the ceiling tiles above your head—it doesn't matter! You can truly relax and try to recuperate from whatever has been stressful. Additionally, you can choose lazy activities that are particular and comforting to you. Even watching a movie is different when you're alone. There's no agreeing or compromising on what to watch. You can watch three cartoon movies in a row, if you want, and eat chocolate ice cream while you do it. No one is watching you. If it makes you feel less stressed, do it! Any silly little thing becomes a welcome relief.
There is also the benefit of not having any distractions or noises to bother you when you are alone. You can sit down, take a breath, and organize your muddled thoughts. You can think over your workday or recent assignment and contemplate how everything is going. If you need to make a change in your routine or set a new goal, you can plan it while you are alone and in a nice quiet space. This can potentially decrease your stress levels in the future. The key is getting that moment of calm and clarity.
That's why I think that, yes, the best way to relax and reduce stress is to spend time alone. You do not have to force yourself to keep up with the energy levels of others, you can be as silly as you want in order to relax, and you have enough quiet and solitude to gather your thoughts and plan your next steps.