If you love longan (pronounced as lamyai ลำไย in Thai), you would be be able to find the most delicious longan in Thailand, specially those grown in the province of Samut Sakhon: 
Example of a longan tree where the fruit is usually harvested once a year
The size of the ones grown in Samut Sakhon are large, the fruit is sweet and usually you would not develop cough unless you have eaten lots of it. If you are already coughing, then you need to stay away from longan as this fruit, as delicious as it is would aggregate coughing.