It is sometimes difficult for a newbie to know whether a spam attack is in progress. It's too late to do anything when the transaction is send with a standard 0.0001 fee. So it is good practice to check the network before sending. An easy way is to check:
https://www.blocktrail.com/BTCFollow the optimal fee specified on the page, can't go wrong.
In recent months the pending transactions are far more than the limit of current block size.you could see the bar in here Cointape.com . So the senders have to pay more than recommended fees to get the transactions confirmed!