Leverkusen, who left Michael Ballack on the bench despite his goal in their midweek Europa League win, looked to be cruising to an easy victory with goals from Eren Derdiyok and Simon Rolfes either side of half-time.
But Bremen, whose coach Thomas Schaaf is under mounting pressure with the team battling to avoid the drop, roared back in the final minutes, pulling one back in the 82nd minute before Proedl headed in from close range.
The draw leaves leaders Borussia Dortmund 12 points clear at the top on 58 points following their 3-1 win at champions Bayern Munich on Saturday, with Leverkusen second on 46. Bayern are fourth on 42, two behind Hanover 96.
"The team is obviously bitterly disappointed," Leverkusen coach Jupp Heynckes said. "They should have left the pitch as clear winners because we had Bremen on the ropes for 70 minutes. We dropped two points because we were not clever enough in the final minutes."
KIESSLING BLUNDER
Bremen keeper Tim Wiese was outstanding in the first half, twice denying Leverkusen from point-blank range, but he was helpless three minutes before the break when Swiss Derdiyok rose above two Bremen defenders to head in.
Rolfes slotted in from the left midway through the second half before Stefan Kiessling scored an own goal under pressure from Per Mertesacker eight minutes from time.
Piling players forward, Bremen were rewarded with a confidence-boosting equaliser from Proedl. They move up to 25 points, a point above the relegation play-off spot.
Leverkusen ended the game with 10 men after Arturo Vidal was sent off with a second booking.
"If you are 2-0 down then this draw feels like a victory," Bremen coach Schaaf said. "Right now, in the situation we are in, we need any point we can get."
VfB Stuttgart improved their chances of staying up with a hard-fought 2-0 win at Eintracht Frankfurt despite playing most of the game with 10 men.
Stuttgart, who had captain Mathieu Delpierre sent off after 15 minutes for pushing a Frankfurt defender before a free-kick, took the lead when Martin Harnik pounced on a goalkeeping error to slot home from close range in the 64th minute.
The visitors added another goal four minutes later through Tamas Hajnal to seal their second win in four games and move up to 22 points, three ahead of last-placed Borussia Moenchengladbach.
Frankfurt applied pressure late in the game but could not break through. They are yet to score in 2011, and this was their seventh successive league game without a goal.
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