Dwindling Skills

I've been back in the USA for a week and I've already forgotten how to convert Fahrenheit to Celsius. If I think about it for a few minutes, I can make a rough conversion, but I used to be able to do so in a matter of seconds. The fact that it's only taken me a week to forget a skill I used regularly in Spain worries me about my beloved Spanish language skills.. now begins my effort to maintain a skill that I will use rarely for the next few months.