First day of advertising a web hosting site on Adwords, I got plenty of conversions (purchases) from search (11), with an average visit duration of 21 seconds. The next few days, there were just a couple of conversions from AdWords, average visit duration dropped to 7 seconds. But there were more pageviews, and I have not changed anything. The ads are in the same position. My business is located in China, and I feel this might be clicks from a competitor.
If they were fraudulent clicks chances are you will be reimbursed if those fraudulent clicks were detected. But overall it can be very unpredictable. Sometimes I have conversions several days in a row and then I have none for a couple of days. Something as simple as the day of a week can influence purchases.
AdWords will detect invalid clicks, so you don't worry about competitors. Your conversions may come back soon if your services are good.
Less clicks can mean the average bid is up that makes your ads lose to the higher bid. Google can protect you from fraudulent clicks, sometimes it is automatically uncounted, but sometimes the fraud charges will be given back daily / weekly / monthly. If you think the clicks is too little, you can change the bid by 1 cent or more then see the differences each day until you are satisfied with the results.