Help me, what do I do in the future

I just played a game where I was having some odd performance issues with my computer. For one reason or another my computer was not really working all too fatst and so my game was running at about 10-15 fps, with random jumps and skips, stalls and stops, you name it my game was doing it. I had already died 3 times because of stupid things that resulted because of either my inability to trade or not being able to react to a situation about 2 or 3 seconds after it had happened. I decided to afk for about 3 minutes while restarting my computer because I knew at that point that I was either just going to be able to sit in base, or just die more. When I came back to my game my adc was saying he was going to report me for afking. Yes I did afk but, I let them know I was going to be right back, and I did actually come back to the game. I tried to be as reasonable as I could with my adc but you know how people are.

I can without a doubt say that everyone has had problems with their computer functioning at one point or another, I would just like some advice on what to do in the future because this was an incredibly frustrating set of circumstances I was put under that to be quite frank, I cannot necessarily control. I still lost a ranked game and now I am tilted because my teammate was grief-ing me for afking when it was not what I wanted to do, nor was it something that I would have done under most any other circumstance.

Thank you