The Spanish champions' hopes of retaining their league title have been dented by the impressive form of their arch-rivals Barcelona.
Barcelona, who aim to win a remarkable treble as they reached the Champions League semi-final and the Copa del Rey final, occupy the table's summit on 75 points.
Second-placed Real trail the Catalans by six points with eight matches to go.
"It has been a lot harder this year and we have had to fight like crazy," Dutchman Sneijder told Real's official website.
"We have played very complicated matches and been able to overcome adversity. Winning the league would be incredible."
Los Merengues will be looking to extend their winning streak to five games when they face Recreativo Huelva on Saturday.
"It's an important match. We have eight games left and all are finals," Sneijder added.
"We must stay on course and try to reduce the lead as much as possible. We cannot suffer any setbacks."